Boy, sure can't say that I do...I stick pretty close to the 100 yard limit when it comes to muzzle-loaders, so bullet drop between the two calibers would be a non-issue to me.
Also, considering both my .58's both will take a .570" ball, and my .62 fires a .600" ball, I'd say trajectories between them would have to be very small at any range...possibly un-measureable as the difference between .570" and .600" is pretty tiny...definately less than the difference between .580" and .620", if you know what I mean.
Of course, "your results may vary", depending on what make barrel you use, and what size ball it likes. Mine's a Colerain, and it likes a .600", and I know others with the same barrel and same thing, the .600 loads best...610"s really have to be pounded down. In a way, my .62 is "only" (!!!!) a .60 calibre. Ha ha only a .60!
Well I know what you are going through...I had to think that over for a long time....58" or .62". But, I have no regrets, love the .62, it's becoming/has become quite popular so no trouble getting moulds, jags, etc. I'm glad I went .62".
Rat