It depends on the camshaft, the deck height (ie quench), induction and exhaust.
As quoted above you need to know these things as its the Dynamic Compression Ratio you need to worry about. A 10.5:1 static CR engine could have a DCR of 7:1 with a BIG cam or 9.5:1 with a stock cam.
I've gotten away with 8.5:1 DCR on an iron headed V8 with .039 quench on 95 Octane and you can usually do better with Alloy heads.
take notice of nod's comments just because somebody runs 11.5 comp with say chi alloy heads does not mean it wont ping with say a different cam etc , camshaft plays a big picture in it amongst lots of other things . a 9.1 static comp motor can have more dynamic comp than a 12.1 static comp motor . there are formulas for working it out . the dynamic compression has to be known not just the static compression .