I would like to see a photo...

Phil Hill wrote:

If highly-skilled, possibly none, but he/she would most likely have to work harder. The 6D has a wider latitude for re-framing by cropping and would be more tolerant of exposure errors. Also the 6D is less susceptible to camera shake in low light because a higher ISO value could be used.

But successful wedding photographers have been using 40Ds for years, so one would need to know more about the photographer’s skills in order to answer your question.

If pressed for an answer, I’d say it’s more likely that the 40D photographer wouldn’t be hired in the first place (in today’s market), rather than the price that could be charged. Again, though, a skilled photographer with a good reputation could easily overcome this.