I'd go for a gtr and run it in rwd. Room for more rubber, stronger engine an the option to go awd again if you want to go around a track fast or you have too much power to put through 2 wheels. There is also the bonus of better interior bits and projector headlights.
There is still plenty you can do to it ie. suspension, build the engine, cage, fuel system, rims, turbos, cooler, exhaust, ecu etc. etc.
You could sink quite a bit of money into a gtst to bring it up to the same level as a stock gtr in rwd, why not start with the gtr and build on that.