W/o opening too large a can o' worms, there is a lot of useful information here:

http://www.bunkershooting.com/ReloadingForBunker.html

I'd suggest one review the whole site, lots of good information there, arrived at through no small expense. Do enough screwing around [testing] at the grease plate/pattern board & shooting bunker & powder pigeon & you can come to similar conclusions.

Also, Lyman in one of their maunals offers some really good downrange ballistic data on lead pellets, the gist of which says that by 40 yards most target sized shot is travelng at similar velocities irrespective of muzzle velocity & if you want to deliver more energy for game or target purposes, use a larger size shot.