How much power is too much?

[siggyfreud]

I'm starting to consider engines to continue my build. I am looking at everything from the 480hp LS3 to the newly available LT4 (640hp) with 8 speed auto.

I'm not building a pro street machine, just going for a fun pro touring setup. I was considering the lt1 for it's direct injection benefits, which has about 460hp and the 8 speed, but it's only about a grand more for the LT4 model.

Looking for advice for those who have driven high horsepower trucks like these. I've had powerful cars, but none without some of the modern aids we enjoy today. I think the highest I got in this truck before was about 380.

How much becomes too much for these old rigs?