I favor the non-padded Vickers sling. I left active duty in '05, and I'd carried an M4 with a non-padded sling for pretty much up to 60 or 70 hours straight... and in my other life, never used a padded sling for hunting (probably max 8 or 10 hours humping a full-sized rifle with frequent breaks or sitting in stands). Frankly, since I've never been in the Foreign Legion and had to march for days across the sands of Northern Africa, I've not yet felt the need for a padded sling.
I guess the caveat here would be that I've never worn/carried a super-heavy long gun for unbearably lengthy periods, but one assumes everyone's tolerance levels may vary widely.
Wonder how much in royalties Larry gets for every one of his slings sold?