How much FWHP should the boosted SHO be set at ?

Theres 2 Turbo ATX’s pushing 400 to the wheels on non-FPS trannies and they have yet to blow up. I say shoot for 450. But I’m not the man putting the money into the project. With the setup he has (And similar to the one I want, except I was thinking 35R) I was looking for 450. The only thing in the back of my mind was the fact that I didn’t want to buy the FPS tranny, whereas he went ahead and did it.