I'm running NGK 7's on 11:1 iron head on 91 octane pokin around town. Will probably go with 8's at the track. Running 7's because that's what the local race shop recommended for that motor and the previous owner said to run 8's at the track (that was when the motor was 13.9:1 CR). I would say that 10's are way too cold for your setup. You'd probably be alright with a 6 or 7 plug.