At 6V, it'll take less than 3A to hit the 90% mark, and I can see my combined current draw to be higher than 3A.
Normally I would agree not to regulate something like a motor, but I think I can afford the 10-20% energy loss (since I have double the energy capacity). Also, I really don't want the robot to slow down as the battery voltage drops, which is another reason I'd like a regulated power supply. The weight won't be a problem, size might be, so I still don't know about that.
I was surprised to see TI making that chip considering it is more a completely module with a PCB and everything. They even gave me a couple of samples (they are about $10-15 a pop otherwise). Though these things come with non-.1" spacing, which makes prototyping bit of a pain.