I also use a 58 caliber. It is a custom that I built myself. It has a flint ignition and a Green Mountain barrel. I shoot patched round ballsover 90gr of GOEX 3-f.
The thing that I like about using the large bore is that it leaves a nice size exit hole. If the deer runs it leaves a nice blood trail.
From what you say about the performance you are getting from your rifle and load, I believe that you have a winning combo that will do nicely for any large game in North America.