I did consider the 6D, but decided for a number of reasons that the 5DIII would be worth the extra cost for me.

If I sold my T2i and associated gear, I could probably get enough to buy a 16-35 f/4 IS. If I paired that with the Sigma 50A and 70-200 seems like I'd have pretty good coverage as well as some nice creative options with the 50.