I never really understood people that say a 8lb or a 9.5lb rifle is "too heavy." I've never served in the military, but I have carried a hunting rifle an average of 2-3 miles each time I hunt. I have hunted with a 6lb 18" Rem Model 7 and a 8.5lb Rem 700 SPS 308. Both have large scopes, so add about 2 lbs. To be honest, I couldn't tell you I ever noticed any difference carrying them. 2-4lb extra weight, to me, is negligible. I'm not a big guy, 6 ft 0, 170lbs. I am used to carrying 40lb backpacks doing backpacking most of my life. I'm 45 years old and I still can do it.
I get that you can carry a lot more ammo with 5.56 and I would probably choose that route, if headed out to war. But, when I hear people say get the 6.5lb hunting rifle with the pencil barrel, I guess I just don't get it. I'd rather carry a few more pounds, knowing my rifle is as accurate as it can be and easier to hold steady. Well, that's just me. To each their own.