Humberto,
Crop factor has nothing too do with telephoto reach. The pixels on subject is a function of true focal length and pixel size. Cropped sensors have traditionally had smaller pixels. More information at:
http://www.clarkvision.com/articles/telephoto_reach/
For reference, see Figure 2 on the above web page. The new 1DX will produce images between that of the 1D Mark II and 5D Mark II on that figure (but closer to the 5DII). This is a disappointment to me. If one wants more telephoto reach, which is common among bird photographers, one needs a sensor with smaller pixels. I was hoping Canon would have come out with a sensor with about 5-micron pixels (between the 1DIV and 7D), so about 30 megapixels full frame with improved efficiency so the light per pixel was similar to that in the 1DIV.
The announcement also says nothing about AF at f/8. In fact, the announcement is ambiguous regarding f/ratio: say maximum aperture then say f/ratio. If they mean maximum f-number, then there is no f/8 AF.
No specification of buffer size.
Does anyone ever use ISO 102,400 on the 1DIV and think the image quality is ok? 204,800 is a joke. The 1DIV collects only 54 photons per pixel at ISO 102400, and that is max; an 18% gray level would be only about 10 photons! With slightly larger pixels in the 1DX, ISO 204800 will be similar--something for marketing to brag about.
Roger