Either is GTG, and a big step up from the 308 in terms of ballistics. That said I reeeeally like the 6x47L. I run 115s @ 3050 in my 27" comp rifle. Insanely accurate, great ballistics, low recoil. Not to mention the Lapua brass is incredible!
Downsides to the 6mm version are-
Shorter bbl life...