Hey madcabbie, I'm thinking of purchasing a GTR too after my Gts-t.
There is nothing wrong with the Gts-t. I had no problem with my car and it is a pretty fast car to get around too.
But either way the GTR is faster, even if you modified a Gts-t to be as fast as a GTR, I don't think you will have the outright handling and grip of the Attessa.
I still have my Gts-t now, but keeping my eyes out for a nice, clean GTR.
Let us know how you go and what you end up getting.
Cheers