[Moppie]

Where in the world are you?

If your in NZ the GTR will get stolen.
The GTiR might not, but people will go looking for it.
Its a rather sad thing to say about NZ, but its unforunatly true.

As for performance both are very quick, and quite evenly matched.
They are both the product of Homolgation requirements for the same class of rallying in Japan, and both compteted side by side.
The GTiR should benifit however from more development work, as it was also used by a UK works team, and if the rules had gone the way they were expected to, and Nissan had had the money at the time it would have become a WRC entry.
As it was the Nissan went broke and the change to smaller bodied cars occured to late.
The GTiR was however quite dominant in the UK in group N and in terms of cool factor and desirablity its better than the Mazda.

Both of course have lots of tuning potential should you deciede to tweak them, and the only thing you should let sway you would be a drive of both cars.
That will tell you which better suits your needs.