Ok, get a Shiningbeam S-Mini, an 18650 cell, a lockblock, and a Cygolite Hotshot. Total weight on bike: about 160 grams. On Medium, the S-Mini will do at least 8 hours or more on one 18650, and you can carry spares at 45 grams apiece if you want. The Hotshot is a monster. Bonus: the lights can be shoved in your pocket if you have to park outside.

Even my DiNotte 1200+ is only 400 grams, battery pack included, and will run at half-power for about 6 hours.

As for superbright being overkill and not really necessary/desirable, I guess it depends what you do and where you ride. In hardcore arterial traffic, it's tough to show up sometimes, and overkill ends up being awesome On a dark lightly-travelled highway, where your eyes can adapt and stay adapted, you might only need a fraction of an overkill Off-roading is yet another world unto itself.