I use 1 x 11.25 for my 308s if I order the barrel but I also have a 1 x 12 that shoot fine.
The use of 168 has changed over the years, mostly since the arrival of the 175's of course. I shoot 168s and will agree that to 600 yatds they are fine and in fact in my rifles they shoot BETTER than the 175s at 600. I recently shot a side-by-side comparison of the 168s and 175 at 600 and 1000 yards. My scores were better by a few points (and many "X"s) with the 168s at 600 and better by 9 points at 1000 with the 175s
600 Yards (6" "X" ring, 12" "10" ring)
GMM 168
Score 199-15X
GMM 175
Score 196-7X
Trajectory data The temps were pretty high, about 90 to 95 (estimate), humidity had to be at 100%, site elevation was 500ASL, wind light from 3 to 6 o'clock mostly with a few quick switched to 9 o'clock.
For the 168's I used 13.75MOA up and .25 to .5 (R) windage.
For the 175's I used 13.75MOA up and from 5.(R) to 1.25 (L) for windage to keep the wind.
1000 yards (10" "X" ring, 20" "10" ring)
GMM 168
Score 188-4X
GMM 175
Score 197-6x
Come-Ups for the GMM 168's at 1000, 36.5MOA with wind up to 2MOA (see, it was a light wind!)
Come-Ups for the GMM 175's at 1000, 34MOA and again up to 2MOA for wind.
168s can make it to 1000 yards but the 175's seem better suited to that distance.