Moving from 50D to T3i or 5D/III. Opinions.

Howdy,

I've been trying to do concert photography in small venues (mostly available light, as flash is seldom allowed), and I'd like to branch out into portraiture. I'm presently using a 50D with a Tamron 28-75/2.8, an EF50/1.8, and an EF85/1.8 as my primary lenses.

Lately, some situations have come up where I:

Need to be able to shoot video.

Would like more breathing room at high ISOs.

Also, while I'm generally satisfied with the results I'm getting, from a lens-quality perspective, I would like to step things up a bit AND gain a little more speed.

My budget's pretty limited, so I've found myself trying to decide between these two outfits:

A 5d Mark III, with my existing lenses (assuming the Tamron still works with it).

-or-

Staying APS-C and going with a T3i with a 24mm f/1.4L and a 50mm f/1.2L.

Are there established conventions in headshot-type portraiture that should push me towards the 5D?

Will the lack of Micro Focus Adjustment (which I use on the 50D) with the T3i present any known problems with the aforementioned lenses?

Two big issues with me, as far as bodies go are: my 50D is really hurting my neck and back (esp. when I've got the Tamron AND a 580 on it); and I wouldn't mind the AF being a little more flexible. Is the T3i a dramatic step down on the AF front?

Thanks in advance!

The Customer

(Alex)