I don’t suppose a 4sevens XM18 mounted to a specially made rucksack would be overkill would it ?
Ha, just looked it up. Cool as f**k. I’ve got motorcycles with less power than that. 
Wouldn’t have to worry about cars pulling out on me, could just vapourise them.
Shadow JM07 is great on a bike. I originally had the neutral but later got the cool white which I find I prefer for this. I don’t bother with the extension tube for my rides - a 26650 lasts plenty for me (though I always bring a spare). I also run a Keygos M10 at the same time. (Neither one on max unless I’m out of the city or its late and not many cars are around.) If I had to choose one I would go with the JMO7 over the Keygos. I like the beam pattern and the side switch is really convenient.
I’ve got both the Pro and sideclicky, beam profile is identical accept the sideclicky version the spill is slightly wider… I’d go neutral white, it’s a much nicer tint and easier on the eyes, and gives better depth perception. Cold white tends to paint things in 2D which can make the depth of potholes deceiving.
The pro version also has some tailcap issues due to a slight flaw in the design, although it can be fixed easily.
If you get the side clicky version try and get the version with a knurled body like in this video, better than the smooth body:
Both are great lights for cycling.
Just a follow up on the comment above about heat and cooling. I assembled a Cree XM-L T6-3C 5000K, with an 8* AMC7135 (Nanjg 105c) in a C20 host for biking and skiing. When I first tested it inside it got crazy hot on high mode, but when you take it outside and headmount even the airflow from walking is enough that it barely gets warm on high. So for biking, even 2800mAh is not going to be a problem due to all the airflow, and I get well more than an hour with NCR18650B cells.
Hi, if you need a throwy light go for a JM07 or C8. Both have quite narrow hotspot along with a wide spill. S3-style light will be almost a pure flooder. I personally prefer a floody light for biking but tastes differ. I would reccommend you to get some decent batteries though you may need to increase your budget a bit. From my experience, heat is not an issue even for a small S3-like light (driven at 2 amps). The oncoming air does its job well.