Performance really depeneds on the size of the piping rather than the brand of the exhaust. Although some may say that the brand makes it more of a quality exhaust.
Yes you can get a 2 door exhaust to fit on a 4 door as that is the only thing that I can see that is not a striaght swap from a 2 door to a 4 door besides body kits.
Here is what I did to mines:
This one is from a fello member that I know on another board that has the stock ITR exhaust on his GSR Sedan. The picture shows that he removed the stock ITR bottleneck also.
