The Quaife will do wonders for your handling, and seeing how you have a GSR, the ITR tranny isn't really worth the extra $$$. Now if you had a LS I would say differently, but I think you'd be happier with a Quaife.

Minus the "valvetrain" you listed, the other mods (all I see are bolt-ons?) should net anywhere from a 10-20 (def. high end) whp gain with a rather large loss on the low-end. Not sure if the 70 mm throttle body is really necessary.

Shingo