Hmmm....interesting topic - as always - and both sides are coming out a-plenty!
Like you, I also shoot with the 7D (used two, for pro concerts until recently) and had NO complaints at all.
But one body began to show its age, and so I had to decide how to replace it.
I did so much research it began to be painful, but a pro friend said, "Try the 6D...you'll be surprised".
And I was.
ISO5000+ is effortless.
The controls are so EASY! And yet there's plenty of customisation available via the menus.
The ease with which I can use it, reminds me of when I shot with a Praktica BC1, 30+ years ago. Or in other words, I feel like I'mtaking photos again...not the technology.
But, enough praise for the 6D.
My point is, I had to buy a new body, because, at the very least, doing a pro shoot with one body is looking for trouble!
If you don't NEED to buy a new body, the 7D is plenty....and I think you know it.
BUT, if you can afford a second body, it's GREAT fun! And for my money (concerts here don't offer a big profit margin!), the 6D is the way to go.
That, and my remaining 7D make a great pair!