if you want to use Sigma glass and want best AF, I would say forget about MC-11 and go for metabones and pure PDAF, you will get much much faster AF and as other person said AF though entire AF area of the camera, you will miss out on Eye-AF, but AF simply is a lot more reliable with metabones.
For sigma lenses metabones works better
for Canon lenses MC-11 works better
It seems like something out of bizzaro world, I know its weird, but that the case.
Pure PDAF is garbage in low-light though....and I need something for wedding/event shooting.