None of these things you mention are mutually exclusive with better MPG and lower emissions per mile from any vehicle

Bigger = heavier.

Taller = more wind drag (and on the highway that's where at least 80% of your fuel goes!)

4WD = more mechanical drive. That's why a 4WD truck will get about 25% less fuel mileage than the identical 2Wd model.

Power = tanstaafl. There Ain't No Such Thing As A Free Lunch.

Doesn't matter if you're getting the acceleration from the batteries. That energy had to get into those batteries in the first place, and the only place it's coming from is from the engine. Regenerative braking is a nice idea in theory, but it's not ready for prime time yet. Or maybe it is? Doesn't the Honda Insight use it? Don't recall now... But regenerative braking is only advantageous in a stop and go situation. Get that hybrid SUV out on the interestate pushing that "sleek" .65 cd body through the air at 75 MPH and spinning all those axles, constant velocity joints, drive shafts, differentials and transfer cases merrily along -- I don't care if it's a diesel, a hybrid, a gasoline-only, or any combination thereof -- it is going to burn a lot more fuel than an "automobile" (mini-van or station wagon) of comparable capacity.

tanstaafl.