Look at the 308 charts on this website. They are using Varget with light and heavy bullets. I am not saying Varget is the best choice.
http://www.accurateshooter.com/cartridge-guides/308win/
If the powder is to slow because of below 90% burn why are they getting good velocity? If 10-15% of the powder is burning outside the barrel wouldn't you get low velocity? I believe real world results before computer generated data. Don't believe everything a computer spits out. Chrono the velocity.
My Sierra manual list these powders with the higher velocity with their 110 gr bullet:
H322 3300 fps
748 3200 fps
H335 3300 fps
The Berger manual list 10 powders for their 115 gr bullet. All above 3114 fps.
Some of the highest fps listed:
H322 3206 fps
H335 3161 fps
Ramshot Tac 3195 fps
Win 748 3241 fps
BL-C-2 3234 fps.
N135 is listed for the 125 GR bullet.
The manuals are conservative. I always assumed that the listed powders that give the highest fps for a given bullet weight are the most efficient for whatever reason. Compare these powders to others close in burn rate.