06 G35 Coupe Vs 06 Mustang Gt

Statistically, your GT has the edge in acceleration (0-60, ¼) over your friend’s G35 stock for stock. With a CAI, muffler delete, and no tune, your friend’s G35 isn’t going to have a noticeable amount of HP power gain. At most, his G probably gained 10-15HP which isn’t going make much of an impact in performance. I used to have a 2003 350Z (287 HP stock) and then added a NISMO CAI, NISMO cat-back, and plenum spacer. Didn’t dyno it at the time, but I estimated the total power gain would be about 30HP. Still not a major impact. Traded that 350Z for a BMW 335i and that was big step up in performance.

Given that you have a Steeda tune and axle back (No CAI?) the HP gain is probably about the same as your friend’s G so you both are relatively the still same.
So basically, it all depends on you and how good your friend is with a manual.