I have a 04 G35 Sport Coupe with a 6 speed, about how much power can the stock trans and clutch hold up to.

 

The stock trans and clutch should hold up to all the power the stock engine can give you.

 

Good answer. And the connection between power and life is a power relationship. Double the power and life goes down by a factor of 8x or more (2^3).

But then again if you're paying enough to put that much power in, you probably don't care.