I own a 1d mark ii and the canon 7d. I am not sure of the ISO sensitivity or picture resolution on the 1d mark iii, but I can tell you that in low light I am very limited with the 1d mark ii...autofocus speed is off the charts compared to the 7D, the only downside on the 1d mark ii is the write speed, of buffer for continous shooting. In my experience with the 7D, it has never failed me when it comes to picture quality and high ISO speeds. But after iso 3200, noise is prevelant, and some clean up is required, especially in color photos. Now as I said before I do not own a 1d mark iii, but I have been watching them on ebay in hopes of picking up one for a good deal, still selling for $2000.00 used....10fps is amazing. you can shoot a stop motion movie, no problem. so if you do decide to sell, I think the only choice is either up or the 7D, especially if you want a good autofocus system as well as high ISO sensitivity, dual digic 4 processors, and high buffer rate.... Good luck...I hope this helps.