There is no specific compression for the engine. Too many variables, like cranking speed, valve adjustment, and throttle position can effect the reading. The numbers you listed look good, the engine compression is healthy.
It's possible the oil rings could be leaking, but not likely with the compression that good. Bad oil rings show as blue smoke under load.
Black plugs can also be caused by rich mixture, poor spark, wrong plugs, or running without a thermostat.