Re: What power scope ?
It takes a really good day with a really good scope to see bullet holes usually @ 500. I wouldn't upgrade just to do that. It would take a lot to overcome that.
However, I shoot often enough at that range and have found that my 20x is more helpful when shooting our 'animal' targets. The various score zones aren't concentric. For the standard ring-type, black in the middle targets, a 10x would be fine. I would say same with steel. Any target where it's as much a sight picture rather than fine points on the target, I would say 10x is high enough.
And, FWIW, I understood what you meant. There isn't a front objective today that is 10mm. So, I assumed you meant the standard 3.5-10X, Leupold variable scope.