What is compression and did you have hardened seats installed for the exhaust valves? If you did not have hardened seats installed then I would run a 50/50 mix of av-gas all the time. That is 50%premium/50% av-gas.
If the timing is retarded from max/ideal due it insufficient octane, more octane will allow the timing to be advanced to it's optimal setting. If the timing is already at the optimal setting, additional octane and/or more advance will not result in more power.The increase in octane will allow a bump in timing, how much depends on what the motor wants.