Lol that's what I get for not following POTN too closely. I thought I read they released a firmware upgrade for the 5DIII and 6D, maybe was wrong. I'll dig a bit. If I have to MF I could have gotten the 2.0x TC.
Edit: according to CanonUSA the last update was 1.1.3 on 4/9/13, so nevermind. I was sure I read somewhere it had been released, oops.
http://www.usa.canon.com/cusa/suppor...01e02480866b1e