If you will be shooting regularily at 1000y (f-class) I would get a canted rail or Burris sig zee rings so I wasn't always near the elevation maximum. Chances are good when you mount the scope on the rifle with a 0 MOA rail, you will be near the middle of elevation travel in the scope. If you shoot a 308/155 to 1000y, your going to be near 30MOA elevation from 100-1000y (approx). Since half of 70 is 35, I wouldn't want to only have 5 more MOA left, especially if I wanted to shoot farther than 1000y.
So, to make a long story short, get a canted rail or rings with inserts.
I will be picking up a set of Burris rings as I WILL need the elevation to get to 1000 as my setup sits now with the new barrel on it.