I have a 5D3 and a 7D, and can't imagine why you are not still shooting the 7D at times. The 5D3 certainly has low light advantages, but in the day, the 7D is still a very capable camera. +1
I am a bit like the OP. I have both the 7D and 5DIII. But since I bought the 5DIII, after a series of tests, the 7D has collected dust. I really do need to sell it. This isn't meant to disparage the 7D, it really is a remarkable camera and served me well for almost 3 years. But, I get why the 7D sits on a shelf when you own both. If you are not reach limited, I would rather have the 5DIII, and, at least from what I concluded, usually even when you are reach limited, I preferred the images from the 5DIII. Even though the 7D is a great camera, I like the images off the 5DIII better. You lose 1 fps. That really can't be too much of a factor.
Anyway, I am interested in what those that own both the 7DII and 5DIII end up doing. I am considering the 7DII as a way to get that extra reach, hoping that the IQ/noise control/etc is now good enough that I no longer prefer the 5DIII images even when reach limited. So far, I have been very pleased with what I've seen from the 7DII.
Back to the OP, I, personally, haven't seen enough to have an opinion, but I am glad you started the thread. I think a number of us upgraded from the 7D to the 5DIII. Some may consider going back to the 7DII or supplementing your kit with the 7DII. It is a good question. But I wouldn't expect the answer to be black and white. This is going to be about marginal differences and preferences. Right now I am trying to not get caught up in the wave and to wait for some good reviews (TDP, DXO measurements---not sensor score, sensogen, etc). I am very happy with my 5DIII and only have issues with bird photography, which is only a small part of what I shoot.