A Cormier win over Mir, coupled with his last 3 wins(Barnett, Bigfoot and Monson) gives him the nudge ahead of Werdum's 5 wins in his last 6(beating Fedor, Bigfoot, Nelson, Kyle and Russow) when it comes to next dibs IMO.
That said, I somewhat think that a JDS/Werdum II could be a major selling point given that JDS's UFC journey started by putting down Werdum and Werdum's path since the JDS loss has included one of the greatest wins in MMA history over Fedor and his visibly advanced striking and physical development.
I also wonder if the UFC may want to give Cormier a warm up fight in the UFC, just in case they feel he doesn't have enough exposure to main event a UFC PPV card. However, they can sell the JDS fight as a clash against the SF HWGP champion who is undefeated and trying to avenge his AKA teammate's losses(that is, if Cain loses again)....
Endgame, I think both make a stronger argument than Overeem, whose record is dubiously padded at best.
MY MMA RANKINGS
HW Velasquez Cigano Werdum Cormier Bigfoot Barnett Mir Browne Nelson
LHW Jones Machida Evans Hendo Davis Goose Teixeira Shogun Mousasi Bader
MW ASilva Belfort Weidman Jacare Okami Rockhold Kennedy Consta Bisping Boetsch
WW GSP Hendricks Condit MacDonald Diaz Maia Fitch Kampmann Ellenberger Pyle
LW Bendo Alvarez Maynard Melendez Thomson J.Miller Diaz Pettis Chandler Grant dos Anjos
FW Aldo Mendes Curran Lamas Frankie Zombie Cub Lentz Kawajiri Siver