I was in the same position as you a few months back. My car already had a Nismo 2 1/2 inch cat back system, but after asking around and reading the info on here I went with a 3 inch system from the turbo back with a high flow cat, Nistune, fuel pump, and a turbo tech boost controller. I put the boost up to 10psi and got 204kw on the dyno with 494kw torque. I talked to my tuner about getting a z32, and he said there was no point until I started chasing more power as the stock one could handle it.