I'm in the market for a new headlight soon. I've been commuting for the past year or so with some cateye and Blackburn blinkies which are pretty inadequate on my commute.
In general, the more battery you have powering a light, the more light you get.
However, since you say you want to use the lights for commuting, you can get by with the short run-time of a high powered flashlight. Other than that, you already know your next light needs to be more than what the "regular" two-cell assemblies provide.
I suspect most commuters ultimately wind up with Li Ion packs that can make two or three trips without recharging, last several years, and usually are water-proof enough.