I am one of the few one here that has experience in all these fields, with some of the fastest cars IN those fields in the area…so these words you might want to listen to.
first and foremost, STS is NOT worth the money, and does not work the way it is supposed to without MAJOR modification to the setup, and even then, is far inferior.
that being said, push STS out of the way, and move on.
Remaining: Turbo companies go in and out of business weekly in the LSx world. some of them look nice, some of them look promising. most of them go in the shitter. ONE kit that i REALLY like for the GTO, that almost makes me want a GTO is the APS TT kit. its an aussie made setup, it is pretty complete, very high quality, and is a fairly reasonable price. There is no way that cant perform. Any other setup is a crapshoot; it may work awesome (if they ever send it), it may be poopy (if they ever sent it).
ATI Procharger: If i did it all over again, this is the way I’d go. Reason being, its a very complete setup, very organized, no cutting, you can keep your car traditionally together, its clean, its proven, and its fast. There are many different upgrades you can get as well.
one thing ive noticed between the two setups is that S/Cing brings with it considerably LESS maintenance than T/Cing a car. While i have a lot of fun in my car, all that power comes with a price. Chucks (Firehawk) car is around the same power level, and as far as the S/C aspect of the setup goes, there is less hassle. Which one is more fun to drive?.. that depends on the person. to me they are both a blast.
people can describe the differences in feel between these setups until they are blue in the face. it wont make a shit bit of difference. you are welcome to come by my place so we can shoot the shit about different setups, and you can take a ride in these type of cars. that is the only way you are going to have a more solid answer in your head as to what you want to do. then maybe we can hook you up with a setup 