Somewhere between 13 and 12:1 AFR will give peak power on most engines. Eitehr sid of these figures the timing will need advancing to achieve similar power. This is due to the burn speed of the fuel mixture being fastest around the 12.6:1 region. If you optimise your map for 12.6:1 and then richen up you will lose some power. If you optimise for say, 11:1 and then lean off, you will likely detonate the engine, so no direct comparison can be made really as it depends how the map was optimised with regards ignition advance in teh first place.