I'd think the Gtst would have the advantage on tigher/slower tracks since its lighter, easier on the tyres, and easier to throw into tight corners... but on the faster/not as tight tracks i'd think the GTR would be better...
Driver has a lot to do with it, roll out a 33GTR and 33GTST in factory form, no mods at all, no exaust, etc... same (good) driver, and i couldn't see how a gtst could beat a GTR... once you start throwing a little money into suspension and light power mods its starts to even out....
my opinion