About the only downside I come up with is that I often don't find my brass, but that's going to happen with any semi auto. Weight really isn't an issue hunting my small farm. Most my stands are less than a half mile walk. I walk a lot though, and a good sling makes what little extra weight not any more noticable than toting a bolt gun.
Far as cold handguards, I am usually wearing gloves when it's cold enough to worry about frostbite. I usually have a rest too though, so my freehand isn't having to be used to support the rail.