No experience with the Berger 68, though 34.5gr Varget / 33.0 H4895 driving a 70gr SMK does well. On the extreme low end and pushing about 3000 FPS, but shoots very well out of a 26” tube out to 300 yds. Hopefully this gives a start point.
RE-17 can get the 70gr SMK up there in speed as well. If you ever feel you have too much throat, just under 3700 is possible (not recommended) out of a 24” tube in a bolt 6CM.