Well if you plan on upgrading later James it isn´t bad to go 2.25". I went 2.25" and I have the turbo on. I´m actually not going to go 2.5 all the way. The OEM downpipe for the VJ20 is 2.25". So go 2.25" have fun...go turbo, still have fun, then go 2.5" in the distant future if your power hungry....who knows, if you decide to run enough boost you might want to go 3" and let the turbo keep the necessary backpressure.