http://www.digitalcameraworld.com …-ii-hands-on-review/#null
"
The EOS-1D X Mark II is designed for high-speed shooting and low-light performance, and you can only achieve this with more modest pixel counts.
Many sports take place in less than perfect lighting, and Canon’s new sensor has an important innovation. The A/D converter circuitry, which translates captured light values into digital data, has now been integrated with the sensor itself.
This shortens the signal path and reduces image noise – not just at higher ISOs but also further down the ISO range. This extends from ISO 100-51,200, which is the same as the previous model, but with expansion settings from ISO 50-409,600 – the highest setting is one stop higher than the old 1D X.
"
