Well, I'm certainly late to the party (I was in no real hurry), but I finally conquered the last tile currently available on Factoria. That tile seemed to be a lot easier than the one before it...I only lost one tank on the final battle. And since I started out from Ocica just two days ago I didn't gain any tank levels between attempts.

Now all I have to do is sprint for level 50 and any additional tank levels I can add between now and the Christmas event to start narrowing the commander gap, which means I can almost fully retire my 4*s, except for the last PoC levels (and I suppose the event tiles as well).