As for the weight issue, there ae a couple of good threads on SyTy.net--a site where all wheel drive turbo maniacs tend to drive over their transmissions. The difference wbetween the smaller transmissions and the 4L80E s like 70 lbs. And that 70lbs is located at the very bottom center of the car, so weight should not be a consideration
Here's one thread. There is another with a photo comparison that I can't locate right now. I'll keep looking.
http://www.syty.net/forums/showthrea...8&page=1&pp=15