"I'd just worry about what produces the best groups out of your rifle and leave it at that. What he was talking about is diminished returns. There does come a point that no matter how much powder you add the results of that powder becomes less and less on the velocity of the projectile and its stabalization in flight. Hence, diminished returns."

Great post. At some point it goes the other way. One of the custom gun makers claimed unbelieveable velocities in their gun when used with 200 and 250 grains of Pyrodex pellets. Toby Bridgesdebunked their claimin an article for the 2005 Gun Digest. He used the Savage smokeless muzzleloader for the testing.The bullet used for the test was the 250 grain XTP. The results:

Three pellets-1,955 fps.
Four pellets-1,930 fps.
Five pellets-<1,900 fps.

"The only increase wasthe dramatic increase in recoil."