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.

Also like already stated, 10 grains can mean the difference of a two inch group or a six inch group at 100 yards. It is why we look for that "sweet load" in our rifles. And as Sabotloader was explaining, if you're having accuracy problems, sometimes looking at the sabot can tell you want the rifle is trying to do. But the main things I always remember is; do not exceed manufacturer's recommendations on powder charges, more powderis not always better, and 100 grains of powder in any rifle is still a stout load.

Good luck with your rifle.