Real 1DXm2 vs 1DX high ISO performance comparison

Some time ago DPR added 1DXm2 to their comparison chart.
There 1DXm2 high ISO performance looked slightly better than 1DX.
The only one strange thing was there that 1DXm2 shots were brighter than 1DX shots.
Actually, it was required in LR to move exposure slider about 0.5 stop down for 1DXm2 and raise it about 0.2 stop up for 1DX to make them equal in brightness and the same histogram distributions.
Some people were telling that this is OK and this is just due to difference in analog gain setting in different cameras for different ISOs.

Therefore, when I got my 1DXm2 few days back I did some tests to check different things including high ISO performance.
For 1DXm2 my primary interest was better AF, especially in in dim light conditions and slightly better ISO, which was noticeable in DPR test.
  My tests were done in dim light conditions using the same EF70-200 F/2.8L IS USM II lens fixed on the heavy and sturdy tripod. Once test done with first camera then it was detached from the lens and then other one was attached to the same lens on tripod. So all test conditions were identical for both 1DX and 1DXmII.

So first set of tests discovered that for the same ISO settings and same aperture value 1DX and 1DXm2 were using  different exposure values,  1DXm2 was doing approximately from 1.3 to 1.67 longer exposure compared to 1DX and this difference was increasing at higher ISOs.

As result I had to do exposure corrections described above for both 1DXm2 and 1Dx to bring shots from them to the same brightness level.
For me this means that 1DXm2 high ISO comparison test presented so far at different sources using the same ISO settings and auto-exposure are not correct source for comparison ISO performance and this would be cheating people around the world.  Definitely, with the same ISO settings camera that captured 1.7 more light by its sensor will have less noise in output RAW files.
On the other hand, this simply means that exposure meter on 1DXm2 does better job compared to 1DX and it does not underexpose shots, as it was the case for many Canon cameras including previous 1D series bodies. With 1Dxm2 shot histogram is now about 0.7 stops closer to the right.
But proper High ISO comparison test must be  done using the same exposure time and same aperture value for given ISO at both compared cameras and only such test could give proper results.

   Therefore, I did another set of test shots, first with 1DX with auto exposure and then for 1DXm2 in manual setting using exactly the same exposure and aperture as for test shots with 1DX.
This ensured that both sensors captured exactly the same amount of light for each ISO .
As result, these sensor ISO performance test shots now could be directly compared.
There were four (4) test shots for each camera - aperture 4.0 for all shots, ISO values 6400, 12800, 25600 and 51200 with shutter speeds 1/10, 1/20, 1/40, 1/80 respectively.
So all test shots had absolutely the same amount of light captured by each camera sensor for each ISO settings.
What I had at the end is something that I was expecting before but could not check that myself until I got my 1Dxm2.

As I was suspecting comparison results were not a  big surprise for me – my old 1DX has slightly better high ISO performance compared to new 1DXm2.
Here are attached snapshots done by Window snipping tool from LR screen at 100% view - left side is 1DX, right side is 1DXm2.   All have the same LR default NR setting, luminous NR sliders set to zero. No exposure corrections – both shot get exactly the same amount of light captured by sensors.
  One real surprise for me was that all 1DX shots are perfectly sharp while some 1DXm2 shorts are slightly blurred. For both I was using one-shot AF mode with one center point surrounded by 8 expansion point.
Both were pointing at exactly the same are on the target, as lens on tripod was not moved while changing camera body attached to the lens. Shots was done using remote control and 2sec self-timer. IS was switched OFF.
This was kind of AF precision test in dim light condition.
I did not do yet AFMA for my lens on new 1DXm2 body and it could be result of that, but that would be affecting all test shots for 1DXm2, but some are more or less sharp and some not and all 1DX shots are sharper than 1DXm2 shots.
This is some kind of disappointment for me and I need to investigate that later.

 ISO16400 1DX vs 1DXm2.JPG (268.27 kB, 1863x760 - viewed 14 times.)

 ISO12800 1DX vs 1DXm2.JPG (323.44 kB, 1872x751 - viewed 12 times.)

 ISO25600 1DX vs 1DXm2.JPG (358.3 kB, 1841x740 - viewed 8 times.)

 ISO51200 1DX vs 1DXm2.JPG (463.64 kB, 1873x757 - viewed 8 times.)

 ISO51200 area 2 1DX vs 1DXm2.JPG (434.88 kB, 1875x762 - viewed 9 times.)

 ISO51200 area 3 1DX vs 1DXm2.JPG (480.66 kB, 1883x756 - viewed 7 times.)