A just jap FMIC kit is a good upgrade, cheap...but will work fine. I had one on my r33 which held 254rwkw no dramas!
www.justjap.com
yeah xforce is pretty common, cant go wrong with them
but Id look at full system, 3" front, 3" dump, (high flow cat isnt an issue if you dont upgrade, unless its fubared!) and 3" cat back