Short answer: 1:12 is fine.
Long answer: 1:10 is a holdover from the 30-06, which fired a 220 grain bullet and was modified into the 30-06 by shortening the neck and swapping in a 150-grain bullet. 1903 Springfield rifles were modified for the newer cartridge by setting the barrel back slightly and recutting the chamber. 1:10 is great for bullets up to 220 grains but faster than necessary for lighter bullets. The 308 picked up the 1:10 twist because that's how most folks were making .30-caliber barrels in the 1950's.
Okie John
