well, there are a couple different scenarios, if you have a 2.2 with the dual port heads, you could even get 2.5 headers for your car, but otherwise i think cats/exhaust and everything is the same, i know wrx stuff is different

 

I believe the optimal size is different. From what I've read, 2.5l cars want 2.25-2.5" exhausts while 2.2l wants 2-2.25" exhaust.