well good luck ive thought about switching a couple of times, but i think i will hang on to the stang as long as ford themselves don't piss me off. anyway between the two, the evo is supposed to be a little faster but it looks like crap. whats the point of having a fast car that looks like crap? the sti looks pretty bad ass and will still smoke almost everything. i considered the sti, its a nice car! go for the sti. i would consider the g35 not as fast but beautiful car.
you can get some stillen parts, like a supercharger for the g35.
if you have some time before you make up your mind there is supposed to be some pretty bad a$$ cars coming out. like the new lightning!