The Army isn't "looking" at 6.8 with any seriousness, and those M14's have largely been replaced by 762 and 556mm AR variant heavy barreled "designated marksmen" rifles.
762 NATO has a place, but not as a general issue rifle caliber.
There is no warfighter requirement for a larger caliber?? And believe me, they aren't shy about asking for more and better stuff.
If 556 wasn't working, we'd have already fielded AR10's army wide three years ago.
My experience is based on Desert Storm and I haven't really talked that much to guys over there now. I did see a recent photo taken in Iraq with a Marine with an M-14, so at least some are still using them.
All I can tell you is that based on my experience, I would prefer to carry a larger caliber than the 5.56. We didn't have to carry them for extended periods, so the weight of the ammo and the rifle didn't really make a lot of difference. I'm used to firing 12 guage shotguns and a 30-06, so the recoil on the 7.62 didn't bother me. Also, there's a lot of new technology on recoil reduction that could be applied to a new combat rifle.