As long the light is aimed correctly, i.e. not pointing in the eyes of oncoming drivers, then go as bright as you want.

For what its worth, my MagicShine 808 is plenty bright enough for me to commute home in the dark out in the suburbs. They say it's 1100 lumens, and I believe it; it's about as bright as the CFL bulbs I have at home, albeit more directed. I point the light so it illuminates the ground about 10-15 feet in front of me.