My buddy Keith ran into a problem with a factory made 6.5x68, in that it had a 12" rate of twist, so was unsuitable for even a 120gr. bullet. It shot fine with an 87gr. or 100gr. HP, though no actual hunting bullets (around here).
He re-barreled to a 9" rate of twist barrel. Seems to me, I re-chambered it for him with his reamer, but that might have been a later, newer barrel yet.
Keith actually loves this round - 129gr. @ 3,200fps. Spotted him shooting an elk with that round - worked just fine.
The 120gr. X bullet (3,350fps) took a cow moose at just over 300yards, hit right beside the white spot, and stopped against her chest hide. Full length. At the impact, she braced her front feet spread apart and refused to take a step - then collapsed.
Good round. 6.5's shine. I have 3, two 6.5x55's and a .260 Rem.