FWIW, I came up with the same numbers as AJ for DCR etc., ASSUMING a .039" thick head gasket. If you have the head gasket info, that would be helpful; with a .028" thick head gasket, DCR bumps up to around 8.2. Should be doable, but moving to 93 octane would help (if you are not using it already).
FYI, humidity will tend to LOWER the tendency to detonate. Some research work in the 80's concluded that going to your humidity levels approximated the same effect as 3 to 4 points increase in octane. So you are REALLY doing something special to get into detonation LOL
