How much head milling = how much more compression?

and then
you find out that with the stock cam, your Dynamic Compression ratio, which is the ratio that the engine actually understands, is too high for even best pumpgas, and so, you gotta pull timing out, and the engine ends up making no better hp, and the torque at Part-Throttle is down, and it now sucks gas on the hiway, because of the retarded timing.
But, I suppose, you've figured all that out, right?
I haven't gotten that far yet. Still in the planning stages.

So far I have been running my Slant on ethanol free pump gas, which is 90 octane here. I can get 93 octane easily, which is actually a tiny bit cheaper, but it is "up to 10%" ethanol gas.