Spencer - the caliber actually matters very little here. Generally, you are best off with a 1:12 twist for a .308 caliber. It is optimum for accuracy for bullets in the 150 to 180 grain range, and will stabilize most 200 grain bullets; and I really don't see much need for heavier pills - particularly in this day of bonded bullets.

In the 7MM, a 12" twist might not quite work with some 160's under bad conditions (cold dense air, high humidity,low elevation); so I think I would err on the side of stable and get a 10". I would order an 11" if it's available, but not everyone makes one.