Welcome.
I've had most people I know state they like the GXP style more then my old 97 GTP, I myself can't decide. I like them both.
I took mine to the local meeting place for the youngsters right after I got it Saturday and the one kid there with a 98 GT really liked the sound of the V8.
Is the only difference between the 05 and 06 GXP the location of the OnStar antennae?