Hey Matt,
Thanks as always for your insight!
Let me see if I can address some of your comments here.
>>I'd try and limit yourself to a 2 cell pack.
I agree, the 3-cell is just OK, but probably too much for some if mounted on the helmet. The light connects directly to and will work fine with the very minimalistic Magicshine 2-cell pack (picture attached), but in that case, you'd want to stay on level 4 or below, treating level 5 as a short-use "boost" mode.
>> These XP-E R4s aren't HEWs are they? I guessing not (those are R5s), but worth avoiding if they are, for a thrower at least.
I am evaluating the XP-E High Efficiency White (HEW) in combination with the XP-G to see what kind of blended beam I can achieve. Since the die size hasn't increased for the XP-E HEW, the spot optics work almost as well as with the non-HEW versions. The main difference being the lack of the dark band around the primary spot and just every so slightly less throw. However, I'm betting that the increased output will make up for the difference in throw compared to the old XP-E Q4 bin that I was using... which, I thought, still had very nice throw.
>>I'd still recommend going for a single LED/triple board for a helmet light.
I'm with you on that one. Coming mainly from the road-bike world, the idea of this light was primarily envisioned for bar-mounted road use, but turns out to be really good bar-light on the trail as well. However, it's still quite usable on the helmet in a lot of situations. Recumbent road riding is a good option, since often the bar mount is impractical, and in that riding position, you can position the light on top of the helmet for good balance. In those situations where you don't want to have anything sticking up above the top of the helmet to avoid catching branches, the light has to be moved way to the front of the helmet. This of course makes low weight an even bigger priority, and in that respect, the NiteFlux guys have everybody beat. Not sure I want to try and compete with that... or even should, since there are so many "flashlight" helmet lights out there.
>>... XM-L is more efficient and there is a far wider range of optics/ reflectors to tailor the beam to an individuals preference. Cheaper too.
Believe it or not, the LED's themselves are a very small portion of the total cost of the light. It really is amazing how much it takes to produce a good housing, and then it happens again in the labor and in the assembly/testing process. So the cost for me was totally not an issue. The efficiency boost is almost not a factor as well, since to get the same usable output from 2 XM-L as compared to 6 XP-E/G, the XM-L have to be driven very hard, compared to the 6-LED scenario, where I can drive them in the peak of the efficiency curve. In the end, the form-factor being very compact and low-profile was most important to me.
>>I would ditch that lens cover with the clear sides - that'd bug the hell out of me if someone on a ride had a light like that, given that it would be impossible to avoid blinding someone with it at a stop on the trail.
I definitely see your point. However the light coming out the side of the lens cover is nowhere near the focused blinding level. It's just a nice diffuse point source of light that can be seen from any direction. You can look directly at it from the side even in the dark without any problem. However, I do have some very thin metalized reflective material with adhesive backing that I cut to size to go over the sides for anyone that wants to block that portion of the light. From every other perspective, however, the clear lens cover is what makes this light unique. On the trail, with the light mounted on the bar, the diffuse light coming out the bottom and sides of the cover, make a very nice ambient environment. You can completely see everything on the ground directly around and even underneath the bike. On the road, the clear cover makes very usable side lighting at night, which is particularly good on the taillight.
>>is there a way to get the light to sit lower on the helmet? That would both avoid tree branch clipping problems and the high CoG that makes helmet lights more noticeable.
I'm using the standard Cateye helmet mounting system, which is quite flexible. You can move it as far forward on the helmet as your vents will allow, to get it "lower." However, if I were using it off-road and knew that low-hanging branches weren't going to be an issue, I'd actually move it closer to the top of the helmet. The rotational inertia (yes I am a geek) is much higher with it on the front, plus if your leaning over slightly in your normal riding position, the out-front position puts more strain on the neck. With it on the top of the helmet, and battery in the jersey pocket, I barely notice it. The Cateye mount is nice because it has small de-tents in the aiming adjustment where you can reach up and click it up or down a notch or two for trimming the aim. When you're stopped and talking to buddies on the trail, you can just ratchet the light nearly straight up and out of everyone's eyes.
Keep those comments coming! Love hearing others opinions.