I think it's really too early to tell at this point. Even the earliest owners have only had their cars for four or five months and the number of options are pretty small. I haven't seen enough before and after dyno results to make me think any one is better than any other.
I have seen that the Injen intake on the 6MT coupe stalls the car out at high speeds, so that's something to avoid.
Personally, I'm waiting for the Nismo parts this summer before I make any decisions. BTW, it's great to have another Az owner on the board. If I have any need for wheels, I'll be sure to hit you first. My roommate may also be interested in some new wheels for his Tahoe in which case I'll send him your way.
this in deference to everyone who insists on putting a load of crap at the end of everything they say' - Dr Tom Dowling