You did not mention which rifle it was that you were considering shooting 150 grains through. The reason I state that is depending on the length of the barrel, a lot of that powder might not even get used up. Shoot a large charge over snow sometime and look at the unburnt powder on the snow.

Anyway, 2 pellets will normally produce better accuracy then 3 most every time. Your rifle from a stress stand point will thank you, your shoulder will not hurt at the end of ten shots, you're less likely tp develope a flinch, and your pocket book will be a much nicer place to look into.

If it ain't broke, don't fix it.

Stick with what your doing... Good luck with your rifle and any hunting you might do.