Congrats, they are wonderful cars, I actually traded a '05 Cyclone Gray GTO in for my SRT-6. Pretty weird, same color GTO as yours and all.
I also owned a Scion tC, traded that for a SRT-4, which I traded for the GTO, which in turn got traded for the SRT-6. Seems like we have similar taste in cars.
Anyhow, I loved the GTO and honestly sometimes still think I made a mistake trading it in, but I do love the SRT-6. SRT-6 will probably get traded for a G8 in a year or two anyhow.
Completely different vehicles. GTO is alot more comfy and has a lot more luxury to it that's for sure! Have a blast with it, awesome that you found one with some nice mods already too!
GTO is about just as fast, has a WAY better aftermarket, but the handling is no where near that of the SRT-6 so it's a trade off.
www.ls2gto.com is a great forum BTW, make sure you turn the factory amps up (do a search for it on that forum, makes a WORLD of difference in sound)!
Feel free to send me a message if you have any questions!