902 heads opinion

452's will get you induction hardened exhaust seats, 902's were flame hardened at best, and probably not even that(sources differ, and I haven't personally tested)

906's flow better(stock), but not hugely so, and 452's seem to show better improvements with less money spent on porting, even if 906's will ultimately show greater performance. Without porting and/or refurbishment, it's practically random chance which is better, 906 vs 452, depending on which has worse seats, core shift etc. S/F.....Ken M