Interesting stuff. As for zener/LM317 regulation, I wanted to avoid that: they regulate by wasting power. They take that extra voltage and burn off wattage as heat. I go slow enough as it is.
Might not be a problem on some rides, but I have a somewhat hilly ride that I take, just recently I hit 40mph on it. [I go more like 10 on the ride back up that hill, maybe ...] All stuff to play around with in due time, the battery/halogen setup I have right now is doing the trick well enough.