All I know is that Mr. Shima, who has had the HKS GT2530 before the PE1420 on his Z32, prefers the PE1420. I have heard from several sources that the GT2530 power curve flattens out above 5000rpm, and according the Mr. Shima, the PE1420 continues to pull all the way to redline unlike the GT2530. I have only heard good things about the PE1420, so I think they are well worth considering... you may want to do more research around the Silvia and WRX boards and see what they think of the PE turbos such as the PE1420 or PE1820...