A 126.7 grain, .45 caliber patched ball will kill a whitetail deer deader than a doorknob out to 100 yards. Unless the hunter insists on going for a through the shoulder blade quartering shot.
When it comes to lead conicals weighing far more than a patched ball does, it makes little practical difference between a .45 caliber bullet, and a .50 caliber bullet. The same criteria would apply to .40 caliber bullets in a .45 caliber sabot, compared to .45 caliber bullets in a .50 caliber sabot.
Whatever floats your boat. I always tell new muzzleoading hunters not to get caught up in the minutia of all the possible choices that are currently available.
Any modern scoped inline muzzleloading rifle should be capable of M.O.A. accuracy out to 100 yards with any number of load combinations.
If a hunter had a year of 40 hour weeks at his disposal....
A new, well made, .45 caliber, or .50 caliber, inline muzzleloading rifle without any manufacturing defects....
Said rifle to be topped with 1-8 variable power riflescope containing an illuminated reticle....
Unlimited funds with which to purchase as many different components as he could possibly find....
Excellent record keeping skills....
A 200 yard range to shoot at 5 days a week....
A decent weather station located at the range....
And, a good chronograph....
It is my assertion that by the end of the 52nd week that hunter would have found AT LEAST 20-30 load combinations that would deliver at the very least minute of angle accuracy all the way out to 200 yards.
That's how far along modern CNC manufacturing has brought the muzzleoading industry to, from just 20 years ago. Rifles, bullets, wads, sabots, ramrod tips, everything related to muzzleoading, especially inline muzzleloading, is far improved from even a decade ago.
So, the limiting factor is now, as it always has been; the skills of, the ability of, the quality of the eyesight of, and the willingness to practice of, the individual hunter; not the equipment.