the difference between 5d2 and 5d3 will be the DIGIC 5 processor:
Canon DIGIC 5 Image Processor
The latest-generation Canon DIGIC 5 Image Processor brings phenomenal increases in processing speed and power. Improved chip architecture and algorithms deliver greatly expanded functionality with further refinement in image quality. Improved noise reduction produces clearer images when shooting in low light at high ISO speeds. Enhanced i-Contrast performance adjusts differences between light and dark areas to achieve even more natural-looking results. The faster processing speed also results in faster continuous shooting capability while maintaining full image quality. The DIGIC 5 Image Processor also makes possible a new, highly advanced automatic white balance system. Whereas conventional white balance makes an overall adjustment based on a single type of light source, the new Canon Multi-Area White Balance analyzes several areas of the image to determine whether different adjustments are needed, for example, for the main subject and the background.
Summary:
- Better low light performance
- Enhanced Contrast
- Better White Balance
- Faster continuous shooting
The 1DX has set the limits on the features:
-14 frame per second continuous shooting mode
- incredible 51,200
native ISO — expandable to 204,800
- new RGB metering system, facial recognition and tracking
- 41 of 60 of those autofocus sensors are cross-types, including five dual-cross points at f/2.8
- shutter lag 0.036 seconds?
All due to the DIGIC V chip. The 5D3 looks poised to be a class leading, flagship statement camera in a regular DSLR sized body.
Not saying that the 5D3 is going to have all the features above, but I'd expect it to have most of it. The new technologies are very compelling, the speed bump was something they should have done with the 5Dmk2.