I tried some Autolite plugs in my car... gapped them to factory spec, but man, the wrx DID NOT like the autolites. I drove all the way to F.A.S.T. (Aaron really is cool) on saturday afternoon just to get the NGK's, although if I were to do it again i'd just order them from an Auto Zone for cheaper. I was freaked though... The car had never been so unhappy. I'll always go with OEM plugs now. I had an extensive conversation with Prodrive about plugs and they've never noticed ANY difference with their setups and OEM vs. colder plugs, so I wouldn't mess with it. Especially at this altitude. with slightly less O2 in their, we really aren't concerned about detonation, and putting colder plugs in is just gonna delay ignition that much more putting the timing dangerously early if things ever did spark hot.