I've been shooting muzzleloaders since 1970. I have tried BP and all substitutes almost as soon as they made the scene. Another 20 or 30 years maybe I will have all the answers, but to date here is my take:
1 - Almost every ML'ing gun shoots differently, more so, than high powder rifles.
2 - Every side-hammer BP gun I own now GOEX Black powder shoots better than any of the substitutes and recently I tried SWISS BP and it shoots that much better than the GOEX. All of that being said, I made a gun for my son-in-law and his gun will shoot triple seven every bit as good as BP and that was me shooting both kinds through his gun. I have a friend that is very scientific about and his conclusion is the same as mine - use black powder.
Of course the conclusion is "See what YOUR gun will do with different powders. I guess it is all a given.