gphil,
As background, I have been shooting 75 grain AMAX bullets in a 22-243 which has a 1:10" twist. It exhibits superb accuracy at high velocities.
I did some calculations on your cartridge which gave me a 1:9.6" twist rate for average velocities. This may point to the fact that accuracy shooters usually want to go with the slowest twist rate available which will stabilize the chosen bullet.
The other point is that there may be some slight accuracy shift when you try to shoot the much lighter bullets in a faster twist. But each barrel is an individual event and has characteristics unto itself. It might just handle both weights with no discernible difference or it might not.
Choose your twist rate based on the bullets you will shoot the most then test others to see what the barrel likes.
Regards.