Thanks for the suggestions!
It appears that the Armytek headlights are basically "L" shape flashlights that are clipped onto headbands. I am not really comfortable with that arrangement as I can see the lights could be (easily) knocked out of the clips if hit (accidentally) when moving about in caves and tunnels. So these lights are not really a good consideration at this time.
Armytek handheld lights are being looked at right now though.
When you’re caving you want something simple and bulletproof, the FWA3 is neither. People aren’t hating on it, they’re just stating that it’s not the best flashlight for the job. Fine flashlight, just not for this particular task.
hate on: to criticize someone or say bad things about them, in an unpleasant and public way
If you're saying negative things about something, you're hating on them. 
the lights do snap/ clip in to the mount and then there is a very sturdy rubber o-ring that you stretch over the light and hook at the bottom and the light is not going to come out.
+1… Well Said… & Agreed. 
Stating facts about the FW3A is not negative. It is simply the truth.
I know that you live to disagree with me, ShyOne, but saying that a light is not simple and bulletproof is being negative.
Don't hit me with them negative waves. 
I’ve carried a FW1a as my primary EDC for almost 2 years and I have some FW3a’s. I’ve dropped it many times and it can have some issues with contact from serious impacts. It does not have a spring on the positive end and battery positive dents can happen. They are not a reasonable choice for rough and tumble environments. That’s why I also always carry the Armytek wizard as a backup or first choice for certain applications. Always both lights everyday. One very good compact thrower and one pretty compact very floody reliable all around multipurpose light.
Okay, I give. Let’s all hate on the damned unreliable FW series lights.
All-together now…
The OP seems to be overthinking this, its only an 8 hour trip.
Years ago someone recommended these for 18560s, but the OP being in NZ may not be able to get them cheaply
I just checked it with my caliper and it wont fit 21700s 
20.29 x 69.70mm
Why isn’t the OP talking to @PiercingTheDarkness?
Ok so mines are easy but what kind of caving are you talking about? Established caves with at least a marked or improved entrance, maybe some pathways or routes marked and not too tight? Belly crawling through holes (up down or sideways) or in those short wide water passages? Any large caverns/ampitheaters that you'd want to light up? Pools or water concerns?
Personally, a good headlamp might be your best friend if it's not just easier upright walking and a little crouching. I don't really care for most of the flashlight-headlamps with the right angles...much prefer standard types from Black Diamond and Petzl, etc. Petzl has several worth looking at in their line that has the replaceable lithium pack if you don't mind the cost of those and spare packs. Their standard alkaline ones are so-so....Black Diamond is a little better on those and give halfway decent runtimes and beams (although not what we're accustomed to with lithium ion flashlights). There are much nicer and brighter headlamps but they get pricey and often bulky, so these little ones are on the money for many activities. The Black Diamond Spot and Storm are pretty good now with their latest generation...just gonna need a couple spare sets of AAA. The Storm is actually waterproof where the Spot is not fully (water will get into the battery compartment in rain/splash, but it continues to run...tough on batteries, though). Their UI is fairly simple and has both smooth ramping and a side capacitive touch "button", simple center on/off button that works ok with thin gloves...they work well with hat bills as well. Changing batteries in the dark with those isn't too bad with practice/repetition but an accessory light may be needed or at least make it faster. The Storm has a compartment latch (secure but opens easily) but the Spot will need a coin or something to gently pop it open (can thin down a corner of the plastic loops on the headband for this, too).
For hand flashlights, let me throw out a suggestion of the Sofirn C8F and perhaps a companion C8G if you want a little more focused throw at times. You get smooth Narsil ramping firmware on a 21700 cell, a side switch and a tail switch, medium floody smooth beam with great max brightness and decent distance (more than you'll want in almost any cave). They're a little longer with a bigger head than the lights you listed, so maybe that's a deal killer but I think they have a lot going for them. Other disadvantage is that if you are sliding and crawling around, they're going to dig into you and be uncomfortable maybe (unless they're in a pack, on you or pushed ahead of you), whereas the small lights might ride in a pocket briefly and easily. A disadvantage of the small lights is that if you have an oops and knock a light over/off of something, they're more likely to disappear into places you can't retrieve them, where a larger light may foil the cracks and crevices. Sofirn and most other C8 type body lights have stainless steel bezels that you can buy as an accessory for a few bucks...worth considering since those can add a little shock resistance to a head drop that might break the lens. The C8F has three emitters...really a nice light and can run a long time on low levels. The C8G is a deeper smooth reflector and a single emitter so it's got a tighter beam and more throw if you think that could be useful for the caving you'll do. One or two of each or either, two or three extra 21700 cells in the pack...plus the handy headlamp of your choice. Pretty dependable and serviceable.
The Convoy S2 lights are never going to be as wide or floody as I would want for caving but they certainly have their place and would be useful...and tube lights take up so little space. He doesn't list all the specs for all lights but he also doesn't usually do the ANSI thing (some of which is BS but it gives a standard)...he does have good info and you can of course find all that data on this forum for any Convoy light. I might go with one of his other models that has a wider head, though, and uses a 21700 where you can get some more capacity than 18650s give. His M3 lights are fantastic on run time and brightness without getting hot...impressive...but they are a bit heavy and also can cut out due to the weight of the heavier 26650 batteries not getting dual spring support (they still work fine, just may blink or shut off if you bump the tailcap hard enough for the spring to depress and lose contact with the top button...more on that below).
Also, side note, I think I would recommend a light that has dual springs (head and tail) if you think you may have the dropsies. There has been a trend lately of using solid brass buttons on the head rather than a second spring - this is useful for some aspects but in the case of a good drop the dual spring setup may prevent impact damage to the driver, in which case you're likely to end up with a dead light. I've wondered whether a hard drop on the head with those buttons might also be capable of shorting or damaging the + end of cells, too, but haven't yet heard of that happening. Just a thought, though, since reliability is paramount for caving, even if you're with a group or in "tamed" caves.
Also....another note. You may find that color temperatures on the lower end are both more pleasurable and more practical in caves. One reason is water vapor and dust in the air, where those may be present, and the other is just appreciating the subtleties of color and texture in the rocks. Cooler light temperatures are nice for general use above ground but below it can feel a little tiresome on the eyes with your objects are at close distance and/or you're using the light constantly. I wouldn't want to go warmer than 4500K although some 5000K lights are good. Damn sure would not take a cold white 5500+ with me if I had any say in the matter.
Really enjoyed the caving I did years ago....sure wish we'd had lithium and high power LEDs back then!
I don't like the style of these lights.
There is no mode memory.
And there is a lack of technical information for these lights anyway, which makes it impossible to determine lights performance.
No information, no light.
Style is personal preference, no mode memory actually makes me want to buy it (as if i could afford one), lack of technical information is surprising i googled Zebralight, randomly clicked one on their homescreen and got this:
Thanks for the comments!
Yes, in looking at my requirements again, a semi-thrower hand held light would be useful in viewing what is coming in tunnels, caves, drifts, raises, winzes, and shafts. So I'll be looking at some semi-thrower lights as well. When I say semi-thrower lights, I mean a light that is principally a thrower but has some good spill for "flooding" as well.
Yes, I'm aware that there are variations in the Convoy S2+ range. However, these lights seem to have too little technical information in order to determine their suitability for my purposes. Therefore these lights have been eliminated from consideration. No information, no light.
I missed this comment first time round.
Thanks for the comments and compliment.
I will look into the WOWTAC A2S shortly.
Have you seen this one?
The Zebralights that I checked only had the lumens listed, with no runtimes, no candelas and no throws.
This example here seems to be the exception of including runtimes, but still does not quote candelas nor beam throws. I require all these (four) parameters to enable me to determine light suitability for my purposes. So this particular example light here is also eliminated due to lack of data.
Thanks for the link!
Just had a quick look, and it appears this light is definitely a thrower with an (estimated) beam angle of around 14°. So, basically this light is not a strong contender because I'm really after light that are more floodier (does this word exist?). However, I am just starting to consider at least one thrower light for illuminating tunnels etc way ahead to see what is coming. But the thrower light MUST have some decent "spill" to provide some degree of flood light as well.
I don't know (yet) what sort of spill this light has. We'll have to wait for a review of this light to see what sort of beam it really has.
Many thanks for your detailed comments!
Not sure what sort of caves I'll be going into, but at this stage it is likely to be relatively easy going with little or no crawling and little to no (deep) mud and water negotiations.
Looking at Black Diamond, Petzl and others for headlights as well shortly.
Looking at the Sofirn C8* series lights also shortly.
Convoy lights are not really being considered any further at this stage, due to lack of information on these lights. Maybe later on.
Yes. Dual springs within flashlights help with regard to shock absorption in the event the lights are dropped or knocked hard. This will minimize any damage to the lights. I was looking at that. Unfortunately not many lights use dual springs though!
I prefer neutral (~ 5000K) color temperature as I want to see any colored rocks (and anything else) in their correct/natural colors.
I would also caution you to take all the runtime numbers you see with a grain of salt, and look for runtime graphs. Most handheld size lights have a sharp drop in output a few minutes in. It’s rare they can sustain anywhere near their full rated output for more than a few minutes, and most manufacturers are not transparent about that.