The new Canon EOS R5 Mark II is getting plenty of positive reviews. Here is…
Canon EOS 6D Sensor Less Noisy Than EOS 5D Mark III
Interesting test made by Don Marcotte, a photographer with interests in astrophotography. He wanted to know which camera sensor among the EOS 6D and the EOS 5D Mark III produces less noise. The test was made with a rather simple setting: long exposures wit the cap on the lens (no light). Before looking at the results it is best to read Marcotte's disclaimer:
Please remember that this test was designed to determine the best camera for a very specific night photography project. I would expect that no one could detect a noise difference between the 6D and 5D3 for the vast majority of daylight photography. Only in low light conditions would a 6D deliver observably better results.
Ok, the EOS 6D produces less noise than the EOS 5D Mark III. Check the following images:

Above, 15 seconds exposure: Shot using camera store demo units at room temperature. RAW images converted to 16 bit TIFFs by Canon Digital Photo Professional. Created 400px X 400px crops and applied Gamma=3.0 in CS5.
Below, the 30 seconds exposure results:

It is amazing that Canon's entry level full-frame DSLR produces less noise than the much more pricey EOS 5D Mark III!
On planet5D you can find Marcotte's full description of the test along with more informations and a comparison with the EOS 5D Mark II.
Canon EOS 6D price check: B&H Photo, Amazon USA, Amazon Canada, Canon Canada, Canon USA
Canon EOS 5D Mark III price check:B&H Photo, Amazon USA, Amazon Canada, Canon Canada, Canon USA [planet5D via PetaPixel]