There were many changes between the first year 04's and the subsequent (and very similar) 05/06's. Spend the extra and get an 05. Higher compression, yeah, but you'll probably wind up swapping heads anyway. That is, unless this becomes the first car you ever left alone!!! The slickest major power adder is the magnacharger. Easy and clean install and good power gains. From a theoretical standpont, the manual trans cars have better gearing, but according the the factory brochure, the automatics are a hair quicker at the 1320. I've had several 930's and a have a heavily modded SER-V that gets flogged regularly at the local SCCA Sunday fun runs. I find the GTO is just plain fun to drive. More power would be nice (and will be forthcoming), but the car is an amazing package as delivered. My favorite thing is the chassis stiffness. It is not at all like anything GM ever built. The car is very monolithic feeling, does not stand out, has a back seat, a trunk and is remarkably inexpensive for the technology that it has. I, for one, am glad they don't build 'em like they used to...........