About 18 years ago I faced the same decision, I went with a .40...Remember a 3/8 ramrod ain't going down a .36 hole...

I had a custom made .45, decided to build a .54 for my big game hunting...After the 2nd gun was finished I ordered a 13/16 x 42 .40 caliber barrel from Ed Rayle...

I feel that a .40 and a .54 are two must have calibers for a traditional patched ball shooter...

btw...For squirrels, I drop way down to 25gs FFF and it still shoots flat out to 50 yards...