When I think of above-average tacklers at the CB position, I think of Champ Bailey, Antoine Winfield, Charles Woodson, Sheldon Brown, Vontae Davis, Brandon Flowers... those are above-average tacklers. Newman is not even close to being as physical as any of those guys. You rarely, if ever, see him shoot inside of a block from a pulling lineman and plant a running back in the backfield, but all of those guys do it regularly. Maybe we should define what "above-average" means. If Newman is an above-average tackler, then the corners above are God-like at tackling. I'm not saying I would prefer any of them over Newman at corner, but he is an average tackler, at best. His coverage ability is above-average and that's why he is a very good corner, although the Cowboys do need to groom someone to replace him due to his age.
This is what I would define as above-average:
http://www.youtube.com/watch?v=WasjkXTNTfo
I'm not cherry-picking Newman as a scapegoat. I've always like him as a player, but you have to be physical and a very good tackler to play free safety, and your body and frame have to be able to withstand the position. Saying that Newman could play FS, but not for 16 games because he could get hurt kind of negates the whole point of thinking he would be a good fit there. Those are caveats that can't be overlooked, in my opinion.
Patrick Peterson of LSU would make an elite free safety, in my opinion, because of his size, instincts, frame, and ball skills. If the Cowboys were to land him in the draft, I would hope that they would consider moving him there because I think he would be dominant. I'm not sure you want to pay a safety the kind of money that Peterson will get, but he is, quite possibly, the best player in the draft, so I certainly wouldn't complain about it.