if you bought a Viper-Spec T56 it would probably handle any power you could throw at it untill the point when an auto would be faster anyways....remember there are Viper guys knocking on the door of 8's in the 1/4 and reaching up near 1000rwhp on the stock tranny(they dont last VERY long at those power levels but the take it) and i doubt your ever gonna see those levels out of your car...
In the June issue of MM&FF there is a guy with a 95 cobra who has a Tremec T56 6speed. Sept he had bout 700hp and stomped on the porches'n V-12 mercedes.