There are a few things worth mentioning The only way to tell with sabots will shoot best out of a particular gun is to shoot and compare, you can not be sure any other way because of the amount muzzleloader bores vary.
The other point is if you have warm to hot the Harvester often work best in those conditions if you must hunt in bitter cold then the MMP will work better at that point in time. To start with just try both in something close to your hunting conditions if possible.
Also most if not all sabots are made by either MMP or Harvest though a lot are made by them under contract for others.