If you have a hunting rifle then you don't really need a 6.8.
The 6.8 was designed to increase lethality in an M4 pattern rifle over M855 from 0 to 500 meters for SOCOM. It makes a decent hunting round for those who like to hunt with an AR. Makes sense for those states that require a 243 caliber or larger cartridge for hunting rifles.
If you just want another rifle, go for it.
Machine guns are awesome until you have to carry one.