Thank you both. It was down to the 7D and the 1D mk III; while I wasn't able to compare the two side by side, I'm happy with the choice.
Focus wasn't perfect, but I think that was more user error than anything having to do with the camera. I found that many of the shots were somewhat back focused, and I suspect I need to pay more attention to focusing on her head, rather than just the center of her body. Often I found that the white patch on her chest was in focus, with the head/eyes too soft. Stopping down would have helped (it was plenty bright out), but this was the first time out with the new body and I was more interested in checking out the focus capabilities than capturing great images.
An example of back focus (and one of those images that I really wish was in focus):
And then this one is a bit front focused, but at that focal length/aperture/distance to subject (this isn't cropped at all), there's not much depth of field to work with: