I don't have a point of comparison because I have never owned the 24-70. But I do have the 24-105 and have used it on the 7D and 6D.

I'm not sure I would make that trade while you still use the 7D because of the MAJOR difference in low light/high ISO ability between the 7D and the 6D. On the 6D, even a maximum f/4 aperture is adequate for many indoor needs, whereas it was essentially useless on my 7D indoors without a flash. In other words, you'd miss the one stop aperture loss far less on the a 6D than you would on a 7D.

On the other hand, I find the 24-105 focal length range to be very, very useful -- especially on a full frame body. I am willing to trade a little IQ and 1 stop for the focal range.