Fabian Fopp has produced a video that I thought was worthy of interest for those wondering about the upgrade between the two, and who are prepared to look at reviews by third parties. I am not saying this is definitive, but it is an intriguing insight.
I do like his commenting on those who would want to stick with the R5 or move to the R5II and his conclusion seems more logical to me.
Duade Paton is a bird photographer from Oz. Sometimes I disagree with his conclusions or methods, but he makes some good points and his video is a good comparison to Fabian's.
I will note that much depends on what you shoot and under what condition. For those who need high ISO and frame rates there may be some food for thought. Here is the chart from the site Photons to Photos, where the relative positions of the R3, R6, R5, R5II and R7 tell a consistent story.
IMHO, these are both brilliant cameras but may have benefits for slightly different shooting situations.
I had realized that stacked sensors had lower ISO performance and DR for a while, and that is another reason why the R1 and R3 have a much smaller MP count that the R5 series. Apart from the need for smaller file sizes to record and transmit images in close to real time and publish on-line or to magazines, the larger photosites offering a lower density mean the photosites are larger and thus more efficient, and can cope with the loss of efficiency of the BSI/Stacked sensor: there is so much less data to manage for the processors.
If the rumors of the R6III having the same (or very similar) 24MP sensor to the R3 with many of the focusing features of the R5II, that would be a great compromise solution for those who don't need to the MP capacity of the R5 series.
