Thought I'd follow up on this (albeit a year later!) if only for information's sake...
I ended up with the JetBeam BC40 and it was the right choice for my use. Last year's race happened to fall on the night of a new moon with a some cloud cover. On a river, that translates to nearly pitch black once you get out in the sticks. If you follow race etiquette, you kill your bow light if you're following immediately behind another boat, as the shadows you cause and reflections off the carbon paddles can cause the lead boat a lot of problems seeing. It was dark enough that if we attempted to pull out and pass the boat ahead without our light already on, you could barely see ten feet once you left the comfort of their beam. At around ten miles an hour in a narrow, sometimes very shallow, twisting river, you don't want to plow into a stump or a rock in a carbon fiber canoe, especially when you don't see it coming.
The BC40 was awesome. We ran it low (130 lumens) for the duration and it was more than enough. In fact, I duct taped the bezel so it didn't get knocked into high mode by accident and kill our batteries. The race is such that you don't want to stop paddling to mess with batteries, assuming you could even see what you're doing or even reach the light without getting out of the boat first. It gave us plenty of throw to light up the next bend, illuminating the river and landscape for a good 75 yards or more in places. As it turned out, the aim was a little high, so we did not have the coverage immediately in front of the boat that we would've liked.
I mounted it to the bow with a couple of Quick Fist rubber clamps. True hard mounts are sketchy, as a hit from another boat or paddler might cause an issue you wouldn't want. The Quick Fists have just enough give to take some abuse, but firm enough to disallow any vibration. And when the morning comes and it's time to shed weight, the light comes out of the clamps easily.
Because the light needs to be powered on and off at any given time, it has to be done easily with the use of a quick hit from the paddle blade (but without so much force as to damage the carbon paddles). Most competitors who run mag lites or similar with [upward-facing] side buttons can fashion an oversized rocker switch, but with the tailcap switch of the BC40, it was a little trickier. For this I bent up a spring steel Coghlan's Table Cloth Clamp and hose-clamped it to the rear of the light so that the bent part of the Coghlan's clamp contacted the switch when I hit it from above. Simple and effective, however the steel deformed enough after repeated use that it would often take two or more hits to actuate the switch, which was a big bummer. I'll be working on a more reliable (and hopefully hands-free) mechanism for this year, maybe using a mechanical camera shutter release cable and a foot-actuated push-button of sorts. Pressure switches were a consideration, but I haven't yet found one that isn't momentary only.
Although the throw and beam width were great for what we were doing, there's a tradeoff in regards to aim where you have to sacrifice some close-in lighting to cover the distance. For this, many racers will use a smaller light, often a mini bike light or modified headlamp attached to the primary light, aimed downward just ahead of the bow. That light can remain on, as it doesn't need to be as bright, nor does it cast the severe shadows and glare that the primary does when running behind another canoe. I'm looking at the JetBeam BC10 or Fenix E11 as possibilities, with some headlamps as other options.
Thanks to everybody for their input and suggestions!
