I will be using an Xcessive lower intake manifold on my FD and was wondering what is the best stock upper intake manifold and throttle body to use for performance (regardless of emissions)? I had heard the JDM ones are better, namely the Series 7 or Series 8 UIM? What about the throttle body? What mods should I do to maximize performance?

 

95 and later fd's don't have the egr, iirc.
But, really there's no gain from one REW UIM to another one.

RC engineering makes bored out throttle bodies that are pretty sweet. Rotary works makes a POS big throttle body that I regret even mentioning. Other people knife blade their TB's.
All the power is in boost and tune. Save your dollars for stuff that actually matters. You wont get any bang for your buck out of UIM's and TB's.

I think if you took the double throttle out of a 95+ UIM, cut out the internal baffles and slapped a RC big bore TB on there that would be as sweet as it gets for an REW setup.