If you wear a size 16 and buy the Simms rubber studded ones and don't like them I will buy whatever you get for yourself as a backup pair.
Seriously I have a pair of the Simms's "Herman Monster" boots (non sexy, no soft leather, old school style) Freestyle. The newer ones look better. I will NEVER go back to felt and I have fished in it since 1976. Rock solid on grip in area tailwaters, even on the angled ledges with slime. On small round rocks like the Holston has they are about the same, maybe a hair better but not signifiicant.
PS..i bought mine after a blow out of my old Orvis boots on the Big Horn last year. the flyshop there in Ft. Smith just laughed when I asked them at the end of the day if they had any 16's, but low and behold they did, and my luck continued as I had a roll of duct tape in my fishing bag to save my fishing earlier that day.