I would like to see a photo...

Possibly, but not definitely.

In fact - it's pretty much an unanswerable question in my opinion, unless one makes a whole heap of assumptions about the difference between the two images, the gear used to capture them, and perhaps also employs statistical analysis to help.

It's possible that there would be a few discerning buyers that would appreciate the difference in a final image from a 6D with a 70-200/2.8 compared to a 60D with a 70-200/4. It certainly would be possible to create an image that was visibly different all other things being equal (like composition, exposure and so on).

I think the former set-up would afford the creative photographer with some more options, and therefore make it a bit easier to realise the image they might  be after. But, as always, this depends a lot on what the photographer is trying to achieve. It's not possible to say whether this would always translate into more saleable images, but it would most probably give a bit more latitude for creating them in the first place.