Please explain why the 5D Mark III is so much better than the 7D ? I mainly take sports photography and the speed of the 7D is remarkable that the 5D can't beat it. With the dual processor, the 7D is like a work horse. This is almost a $2000 price difference. Isn't it better to invest in better lenses than upgrading to a 5D ? For potraits I use alot of fill flash and the 5D doesn't have a built in flash.