GXPs are nice, and have a fair amount of power from the factory. The LS4s they put in them do have issues with water pumps going bad prematurely. If you buy used, this may have already been taken care of.

Since you're not planning on buying one right away, take your time to do more research and find out if it's really what you want. If you decide it is, start reading about modifications you would want for it. You'll find a lot of good GXP info on LS1tech.