Firstly, the '270kW' from the Holdens is NOT at the wheels. With small mods most SS's are at 220-230kW, only when they get a cam are they looking at 270kW+ ATW. Secondly, yeah the 32 GTR has always been the fastest. Not a huge surprise though, it just has a better power to weight ratio than the the 33/34.
Weight is a huge issue, think of reducing weight as adding power. Commodores weigh over 1800kg, not including passengers.
Stock v Stock the GTR will f**king eat commodores.