Cal
I bought an HKS uppipe but when the turbo came out we were all srprised that the uppie was cat-free. The HKS was slightly wider in the bore, so I suppose that might have helped a little. Performance mods, in terms of speed are pretty scant to be honest. All I have is the Meercat Sports cat down pipe, cotton airfiler, VF34 turbo and that's it (plus map of course). This gives me just over 340 bhp and a baw-hair under 400 ft/lbs torque. It peaks at 1.4 / 1.5 bar of boost; It's pretty quick!
I managed to break a piston so I have since added forged pistons, uprated oil and fuel pump, racing shells and a V8 intercooler. Since adding these, the power-output never really changed but for one or two horses, its all down to the turbo (and the 2.5) really.
John