GT John

Yeah, The auto tranny is a concern. I have read posts that some are running some real HP with the auto though.
I was at my favorite speed shop yesterday and they had just put a whipple on an '05 auto. The shop owner said that they had to send the PCM to whipple for programming and when its returned and installed they said that they were expecting 475 HP.
My comment was that there wasnt anyway thatthey will get 475 HP out of the whipple using whipples tune............maybe 420 HP max. for the auto. We'll see next weekendwhen I go back to the shop.
The only way to get more HP would be to custom tune the car with a Predator or SCT, but that would probably void any warranties from whipple.

For the kind of money that it takes to supercharge or turbocharge one of these GT's properly (enginemods and suspension)and get the power to the ground, a person might be better off to bite the bullet and buy a new or used factory Saleen or GT500 with all the factory warranties in place.

Just my 0.02

2007GT/CS

My understanding is that the stock block itself is good to the 800 hp range. Of course the rods will let go long before that and the stock pistons are vulnerable due to not being forged and the ring land location close to the top of the piston.

I've never heard of anyone with a crank failure (yet) so I can't comment on what the limit of the stock crank might be.