i run a CR of 8.2:1, only 17psi on a zetec turbo, plenty of power, no need to go lower really for my road car.
as said varying CR has an effect as do all the other components really, you can run the CR as high as you like to get the most power out of an engine, but you need to be more accurate on fuel and ignition, could make it awful on fuel and smoothness though. also consider the chance to hydrolock the engine if you go too high like on drag racers.