Prochargers are good. Magnachargers are good as well. Vortech and Kenne Bells are good, too, but I think of them more as Ford vendors than anything else. Vortechs always used to push the head gaskets out of the FoMoCo 302 V8.
If you go to
http://www.magnacharger.com -- go to the pulldown menu that says "Quick Site Navigation" and go down to GM 2004 LS1 GTO and download the PDF from there. Its a step by step instruction manual -- and it is really, really well done. With one of their units at reasonable boost, you're looking at close to 500/500 on 91 octane pump gas. Don't remember the price off the top of my head, but you're probably looking at $6K or $7K at least, plus installation if you're not going to do it yourself. What's nice about this unit is that it's intercooled. Can't do any better than that for bang for the buck.
As for turbos, I just don't care for them. They're much more complicated than superchargers -- and the on/off nature of the boost is kind of a pain, particularly with a manually shifted car. You can get around that somewhat via twin turbos -- one smaller unit for smaller shots of fast responding boost -- and another, bigger unit for higher top end -- but life is complicated enough.
That said, your best bet is to simply wait a few months and hope to purchase an '05 with heavy discounts. It's a bit of a risk, but if it doesn't pan out, you can always go to Plan B.
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