[Trevor]

The 6-speed driveline is pretty good up to about 590-600 AWHP. About then you should brace the bellhousing if you're going to be launching the car. After that...ummm....yeah. It's solid.

The iron 6-speed T-Case is about bullet proof.

5-speed wise the aluminum T-case is the limiting factor. Not sure of an absolute power number but I would (personally) be weary of launching a 500 AWHP car with an aluminum T-case. You can get a billet T-case which holds up just as well (maybe even better than) the 6-speed t-case. T-Case brackets aren't exactly a proven fix. I wouldn't trust one to hold together an aluminum T-Case on a 600+ AWHP car.

5-Speeds have split bellhousings occasionally too but they seem to take more launch abuse than the 6-speeds...so that's good.