Upgrade to 6D from 7D ?

It's not that the system I have now isn't doing its job, it's just that I notice lately that the image quality of my 7D is no longer up to par with the newer camera's and I always want to get the best (within budget). For example, when shooting my kids indoor with my 7D and NEX6, I get cleaner and sharper pictures from the NEX (with Sigma 30/F2.8 wide open) than I do with my 7D with the 17-55IS wide open.

So that's why I'm feeling the 7D is a bit lagging behind in the image quality department, especially for indoor shots. And this is what makes me consider going fullframe with a very nice, sharp indoor-lens.