The XinTD X3 is a nice tourch with a large reflector and good design that allows many different battery types to be used. Although I admit, I’ve never seen it as a host before.
Something like the X3 or maybe a C8 would seem to fit the bill, although there really is no shortage of torches to choose from these days. Addressing a couple of your points more directly:
Heavily driven This means different things to different people. But you may want to decide how you want to drive a light, then look at available drivers. Personally if you are using an XP-G2 or XM-L2 then I’d say “heavily” driven is 3-5amps.
Heat dissipation well the key things here are; material, mass and surface area. So assuming you are going for an aluminim light and not a stainless steel one, material should be fine. It’s then a trade off in physical size & weight vs mass & surface area. Your intended use should really decide this. Small lights can be made to have huge output and lots of heat, but if you only use them in that mode for 30 sec to a min at a time, it’s no probs. The issue comes when you need to leave it on for 20+ mins at that output level. Basically a small host is just not going to cut it. The flip side is, how pocket friendly and portable do you want the light to be?
One thing, you’ll be wanting a Direct Thermal Path for the LED. So make sure the LED star is a Noctigon or SinkPad II.
Throw This is dictated by LED size vs reflector size and total reflector size. E.g. if you put an XM-L2 and XP-G2 in the same size reflector, the XP-G2 will throw further because it has a higher surface brightness and in terms of ratio is much smaller vs the reflector. The downside is, a smaller hot spot, less bright spill beam, lower lumen output and often a wider contrast between hotspot and spill beam. This is why the old XR-E still makes a great thrower today, so long as you don’t mind the pencil beam.
Along side this, simply making the reflector larger in diameter will also increase throw. Hence why a C8 out throws a tube light, even with the same emitter and driver. Reflector depth won’t really affect the throw, this affects the size of the spill beam and the intensity of the spill beam.
If throw is important you may want to look at de-doming an LED. This can significantly increase lux readings. But of course there can be downsides.
And lastly the other option is to use some kind of TIR or aspheric lens instead of a conventional reflector. High lux readings in a compact size can often be achieved, but can end up with the torch being less useful.
Runtime Well this is going to be affected by your other decisions. But basically there are two angles to look at this. It’s easy to get long runtime by just using a high mAh power source. But you may not be able to get the high output and lux by simply doing this.
Meaning, 1x18650 will typically give you 2600-3100mAh. And can support fairly high amp draw. But the longer you use the light, the less able the cells will be able to deliver the amps. So it’s likely to fall out of regulation and max output pretty soon. So if you will be happy with a long runtime on a lower output, then a single 18650 will work fine. But if you are wanting to sustain max output for longer, then you’ll need to look for other options.
1x26650 will be a step up from an 18650, more amps. So should hold regulation longer and with longer over all runtimes. But you may still find if you are driving it hard enough, that a single li-ion of any type just won’t keep up with the voltage demand. That said, there many lights that use 2, 3 or 4 18650’s in parallel to good affect, but this is because it spreads the demand over all the batteries, so they don’t suffer the voltage sag the same as a single cell light.
Or you need to look at running in series. This config means you will not suffer with a voltage drop as easily, as two cells will always be providing more than enough voltage. My hunch is, that li-ion in series is likely to produce the best regulation at heavy amp draws.
Of course, multi cell lights then mean larger and longer lights. So it’s always a trade off. 