If you like AWD keep the rex, you will probably be quicker in it because of this. If you want RWD (or IMO a real sports car) test drive the two and then decide. I use to have an JDM s15 and picked up a 33 4 days ago, i'm still deciding which one i like better. The skyline is better day to day though for sure, but the great ocean road will be the test.
Also the JDM s15 had extra 30kw, factory boost gauge, digital climate control, rear wiper, folding mirrors, different badging, different colored interior trim, no gay reflectors on the rear bar, different tail lights, xenon headlights, and a 180km/h speedo. There may be some other minor ones.