For strictly deer and black bear, at 65 yards, I think any of those calibres will do good. (why only 65? a good rifle should get you out to 100...or are you going smoothbore? My Brown Bess, smooth bore, will keep them on a paper plate at 85 yards)
Personally I like a bigger bore just to make the gun lighter. !! No kidding. And, I just plain like big bores. I also figure you can always load a big bore down for light game, and get better results than trying to load a small bore up on big game.
I think in your situation I'd go .58, there is lots of .58 stuff around, and it's a really nice size. With a light/medium load it will work great at 65 yards on deer and blackies, but if you ever had a chance to hunt bigger game you'd be all set. (not saying a .54 doesnt' work great on big game) But if you just plain like the .60 and .62" bores, go for it, that's all the reason you need.
I just ordered my dream rifle, a Jeager, and I chose .62" because I hunt Elk, and we have some pretty giant Mule deer also. I almost went with .58, because I already have a .58 slug gun and a ball mould, but I have a dream about going to Alaska some day to hunt Grizz (not some giant 1200 pound Kodiac, just a medium sized bear) and figured .62 would be a little more better for that. The Alaska hunt may never happen, but it's something to....dream about.
On Colerain barrels, the kit I'm getting from Track of the Wolf has that barrel (swamped) as standard. You might want to look at their kits. The Jeager from the Track comes out about $100 less than a kit from TVM, if you add a Colerain barrel. The Track kit also comes standard with a best quality lock, whereas with TVM upgrading to a better lock is $40. The downside is that the TVM kits are more finished I believe, the Track kits more "in the rough", so there's a little more work involved with the Track kit, if thay makes a difference to you. Having said all that, I don't know if they have kits for the paticular gun you want to build. !!
Anyhow, this Jeager kit, with swamped Colerain barrel came out to about $679, whereas a most of the TVM kits are $550, and the Colerain barrel is a $200 option, which brings you up to around $750, add the better lock and you are up to almost $800.