When comparing image sensors, either CCD or CMOS, the system is essentially a box where the input is light and the output is an image based on the light that is seen. The service provided by the sensor is the conversion of light to a digital image measuring light energy. And here hits physical limitations the abilities. Increasing the count of the pixel does not increase the measureable light. In other words: The larger the size of a pixel the better the ability catching (available) light (and the dynamic range).
Sony´s engineers confirms this physical fact, when they were asked why to put a 20.2 MP sensor into the relatively small 1” sensor of RX100 :
“It’s true that increasing pixel count increases noise. But since we manufacture our own sensors, we can easily tweak sensor specs to suit specific needs…..”
Knowing the correlation between Pixel count and Sensor size I reviewed my archives to find high Iso images when having the Nikon Df for a period of time.
There were some occasions like in the church or shooting night shots, but statistically I shot maybe 20 pictures out of 3000 with ISO higher than 3200.
I have to admit shooting with ISO 12800 is a nice feature to have but its like taking a sledgehammer to crack a nut. Some might need it but I am a streetshooter and I am okay with max ISO 1600.