All these 35mm DSLR's have pretty similar IQ at reasonable ISO's.
Nikon D800 | ISO 100 | 1/100s @f/11:
Canon 5D Mk III | ISO 100 | 1/100s @f/11:
... and that's at 800px web size.
Inevitably, someone's going to wonder why I severely underexposed the photo & then lifted the exposure; rather than getting into the logic of why I did that, I'll just post the following comparison, where each camera was exposed so as to not clip the red channel in the sky near the sun. Shadows were then lifted to reasonable levels for viewing:
I don't know what you do to your files but my 7D even when heavily processed, still has enough detail to make a full-res print.