The 6.5x68 will have similar performance to the 264 Win Magnum generally recognised as a good long range sheep and deer cartridge.

A German friend of mine used the 8x68 which would be close in performance to the 8mm Rem Magnum. He used his 8mm on red deer and chamois.

I have not used either of those cartridges myself but they would perform as good as the more common 7mm Rem Magnum or or 300 Win Magnum cartridges both of which give about as good as it gets on hoofed game.