I ran a Marshall 1960a cab with my Mark III and it never did it for me. I swapped out 2 of the GT75s for V30s in the cab and it was night and day. A much fuller sound, lost some of the high end, but filled out so much in the middle and low end I never cared. I wasn't a big fan of the highs response on the GT75s by themselves anyway.
I should also add, I traded the 1960a cab plus a little cash for a Mesa Traditional 4x12 and have never regretted it. I do miss the mix of the GT75s and V30s, but the Mesa cab handles the low end better and it's so much tighter than the Marshall ever was.