For macro, birds, and action, I would think the 7D would be great, with the crop factor an advantage.
The 6D has better image quality in low light. In very good light and low ISOs, you can get good results with a crop and sharp primes.
What glass are you using? Do you have fast primes, and does low light performance matter to you?
If you want better low light performance, you will get it with the 6D. I am skeptical about the usefullness of the camera at super high ISOs, unless you don't mind losing detail. It does give you much better output in low lighting and high ISOs than you will get with a crop. Personally, I like to keep the ISO at below 6400 on the 6D, but prefer to keep ISO below 1600 on crop.


