My experience is that many (if not most) folks who try the 2-7x35 FFII fail to mount it for optimum eye relief--which at 7x is the same as the FFII 3-9x at 9x. I know this because I've actually measured the eye relief in many of each. Since the exit pupil of the 2-7x on 7 is slightly larger than the exit pupil of the 3-9x is slightly larger, this result in a larger "eye-box."
Otherwise, the major difference between the scopes is the length of the tube--which is why many can't manage to mount the 2-7x for optimum eye relief on 7x. It's pretty easy to do on a short bolt action, but not so much on a long action.
But this is mostly irrelevant, since Burris discontinued the 2-7x a couple years ago.
