Only thing that comes to mind right now for a quick on/off unit is the Light and Motion Vega but it has 4xAA NIMH soldered to the head unit. It is a quick on/off from all the reports I've heard off but it's brightness is somewhere in thr ~85lumen range IIRC what other flashaholics saying before. I'm not sure if you can mod the unit to go brighter. The unit is a bit top heavy and given your speeds and lighting areas from pitch black to city bright it won't be bright enough for that ~3-5second heads up hazard-to-reaction time.