No, no, no... don't listen to him. 2.5" isn't too big. It's bigger than what most of the guys here run with HRC kits, but there's no good reason to redo all of your intercooler piping to be like everyone else. I ran 2.5" piping with a .48/.42 T3 turbocharger and Starion intercooler and the performance was very good. When I went down to 2" pipe, the car was noticably slower. I ended up putting the 2.5" piping back on. I think it maybe had to do with the turbocharger spinning faster and operating within a higher efficiency range. That's just a guess though, as I did nothing to verify that guess.

The point is that 2.5" piping isn't overkill and will work great with your turbo. There's nothing significant to gain by decreasing the diameter of the piping. It'll also leave you some room for growth and save time and money.

Also, don't listen to siueclipse... he's not very technical and sometimes gives advise on topics that he's unfamiliar with.