You wouldn't do six or seven because he wouldn't accept it. Why talk about terms that have no reasonable chance of being agreed to?
The top tier backs make $15m+/year. Mack at $9-10m is clearly second tier, at two-thirds the cost of the top tier backs. If you won't go that high then the only other option is to let him walk in free agency.
Is 9 really the market for a guy ranked 10ish that isn't a involved a lot in the passing game. Only 4 RBs make 9 or more. I'd do 6/year, 7 tops. I really don't see a lot of teams backing up the Brinks truck for him. If he ended up with a team that had a poor OL, that could be a career ender.
Part of that is Carlson , he's most definitely the real deal and switch hitter to boot. If he doesn't start the season up north he will be there before the years out. Regardless who they go with the Outfield D will be better for it both with Ozuna and Martinez being gone. I also like the signing of Brad Miller for left handed bench bat with power. I also like the balance in the pitching , wont be RH dominate we have plenty of LH talent to go with.