there are a lot of differences between the gsr and itr motors... stronger rods, raised redline, higher compression pistons, a different head design, stronger valvetrain, more agressive cams, etc.

If you plan to turbo, none of those parts (except a few of those in the head) actually help you. So if turbo is coming, don't waste your money on a type r motor. It can be turboed with some success, but its certainly not ideal.