are you talking about stock or rebuilt 700r4 units? ive done quite a bit of work on a supercharged (12-15 psi) 383ci camaro, that runs on mickey thompson et streets, and its a full weight car (close to 3500lbs). after grenading 3 700r4's with 'performance rebuilds' my buddy opted for an artcarr built 700r4 (guaranteed to 800hp) and he hasnt had another tranny problem in the almost 3 years hes had it. im not saying the 4l80 isnt a good option, the 2 main reasons i recommended the 700r4 are cost as its pretty much the cheapest of the gm 4spds and the other is that i can vouch for the quality of artcarr's 700r4.
of course for the ultimate cool factor the supra 6 speed, would reign supreme. alot of work, but very cool. of course, shifting in traffic sucks.