what he said.... its generally accepted that the standard airbox with a high flow filter will give the best performance especially on the later facelift model. that said the induction noise from a pop charger is nice and the performance difference really wont be noticed so i guess its up to you as to what you want.
the MUST have mod is a stubby Aerial
PM steve at Redline
http://www.350z-uk.com/topic/62006-350z-honda-rdx-stubby-aerials-in-stock/
oh and may i be the first to say