all things being equal,(driver, both stock, etc.) the wrx sti would smoke a GTO. IIRC the sti does 0-60 in the 4's, and does the 1/4 in the 13's. I imagine the phenominal 0-60 is due a lot to the AWD.
That said the sti is lighter, and lacks many of the ammenities that the GTO has. It is loud as anything, has a harsh ride, and last year didn't even come with an audio system. It's like the Acura Integra type-R all over again. Comparing the two cars is apples and oranges in a sense.
I was going to purchase an STi, but in reality it probably would be impractical for me due to the harsh ride and loud cabin.
Let me sum it up this way, my father would never be cought dead in an STi, it is very boy racer, is loud, rough riding, and basically a street legal rally car. On the other hand, my father loves the interior and ride of the GTO, says its very comfortable etc, and loves the power he gets as an added bonus.