If you look at the Barnes reloading manual you will see that there velocity increase over 100 grains of powder. I think they use 26 inch barrel or maybe 28 inches to measure velocity...use whatever charge shoots best in your firearm.

I generally use 120-130 grains of T7 FFF with fantastic accuracy and not in just one rifle. Changing to the FF version doesn't make much a difference. If it's cold weather I generally shoot the FFF version...