Here's my current favorite combo for small size: Aleph 1 head with new style FB1 (TWOK w/Nexgen 1000). It is next to the regular full Aleph 1 for size comparison.
The unit is very bright, easily one of my favorite lights. I swap the bodies depending on whether I need functionality or small size. I would recommend this configuration, but you may go for more runtime with a lower bias. Personally, I switch my rechargeables every day so I like this combo.
Side note: If you're going to order your own body, I'd recommend jcciv. Great service.