I also just have the 400L as a headlight and a 140R taillight. I think anything brighter than the 400L is more for off-road riding as the beam patterns and power may blind oncoming traffic. I've had the 400L out on unlit, winding roads at speeds up to ~30 mph and never felt like I needed more light. Like others have said, I operate on medium power when in traffic.
By the way, what happened to Magicshine?