I found that with a CT26, upgrading the intercooler (57 trim turbo) lost me almost 2 psi boost pressure. So, the stock system is adequate for a CT26 (although there is one pipe that is a bottleneck). With my SP6262 T4 setup, the larger intercooler was needed and 2.5" piping with a 4" intake pipe work excellent. Going larger than 2.5" I think would cause me performance issues because I would lose pressure in the system (my intake/exhaust ports have no porting and am on stock cams).
You have to match the pipes for the engine and turbo really. And even the turbo, a lot don't think about it properly. You want response and power, not just pure power with no response or vice versa. I have found from reading and from actually having it on my car that the 6262 is an excellent match (with a .68 ar). However, the response is a little slower (as in turbo lag) as I don't really hit the power until 4200 rpm at which point my wheels will lose traction in 3rd. A QSV will solve that by moving my spool time sooner.
If I was a 2j, then this discussion wouldn't hold the same as they have a higher redline (the 7M doesn't like higher than 6200 if your being "safe" with the engine).
For intake, I wouldn't play with upgrades unless you were going to swap out the CT26 for a larger flowing turbo. I found it hurt more than helped. The stock intercooler and intake piping is adequate (note that I didn't discuss the little restriction that apparently is in the 3000 pipe because I have the HKS 3000 pipe replacement with is actually bigger than a stock version.
