Upgrade to 6D from 7D ?

Sounds like the system You have is doing the job, you say you don't get

much use out of it otherwise.

Doubt your clients could tell any difference in the change to FF.

They say that the change from a 7D to a 6D would be a step backward

in camera function and handling, the 6D is modelled after the 60D.

You would also have to spend more money on the 24-70f2.8LII

to keep up with the low light performance you need.