Rc????
Rc???? 
Presumably you mean Running Compression? Most commonly referred to here as Dynamic Compression. The answer varies based on what cam you are running, specifically, when the intake valve closes and captures the charge in the cylinder.
Most often, 8.5:1 to 8.7:1 is the sweet spot, but depending on your build, you might be able to tolerate a bit more. Higher altitudes of course have less air density, so that may allow you to run more too.
Check out RSR Advanced Dynamic Compression Ratio Calculator which should steer you in the right direction. Just be a bit conservative, and you shouldn't have to mess with expensive octane boosters or retard the timing to make it run right...
Most often, 8.5:1 to 8.7:1 is the sweet spot, but depending on your build, you might be able to tolerate a bit more. Higher altitudes of course have less air density, so that may allow you to run more too.
Check out RSR Advanced Dynamic Compression Ratio Calculator which should steer you in the right direction. Just be a bit conservative, and you shouldn't have to mess with expensive octane boosters or retard the timing to make it run right...
