Hey all LL
I had the chance of testing a pre production model of Canon 5DsR up against my 5DIII.
Testing can be done in many ways, I tested the way I would use the cameras in real life, and this is my findings: (I only shot RAW not any jpgs - sorry but I can't post any files, you have to take my words on this)
Low ISO / Sharpness:
The 5DsR is much sharper than my 5DIII, this is no surprise and the difference is like applying a sharpening to the 5DIII of 100/1/3 in Photoshop.
But it seems like the 5DsR has a much better contrast and color depth, it kind of has a more 3D look compared to the 5DIII - for me this is very good news.
Noice is very well controlled, and you can pull the shadows a lot and still have a clean file (see later)
High ISO:
Much to my surprise the 5DsR is as good as the 5DIII up to ISO 6400, perhaps even a little better. I did not test 12.500.
I can be little hard to judge as the files have different sizes, but developing the 5DsR to the size of the 5DIII give a really good impression.
I would happily shoot 3200-6400 ISO in hand held low light situation with my 5DIII, and will do the same for the 5DsR - as a reference I would no go to 1600 on my 5DII
Night shot:
I did some long exposure testing (city) and som high ISO too - and the 5DsR are on pair with the 5dIII. However the 5DsR have a different color look (more warm) and I kind of like the 5DIII better.
Noice is very well controlled, I could pull the exposure in Lightroom up to 4 stops and still have a usable file. The 5DIII I could pull about 2 stops. Very clean shadows, but pulling 4 stops shows that is is still a Canon camera (magenta/green cast).
Color:
Much more color contrast and color dept in the 5DsR, however on long exposure the 5DsR seem to have different look.
Highlights:
The highlights are about the same, perhaps the 5DIII is a tiny bit better of controlling blown out highlights (lamps at night)
Moire:
To my surprise, it was kind of difficult to get some moire in the 5DsR. I had to shoot different fabrics / patterns several times to finally get moire (shot with 24TS) - it was actually easier to get moire on my 5DIII
Hand held:
I did not play around with the new 5DsR settings, but the 5DsR shutter is much more soft. However I can shoot handheld (24-70 at 70) and get consistant sharp images at 1/45s with my 5DIII, I had to go for 1/90 for the 5DsR, so that is a setback.
Other Findings:
The 5DsR appears to be a slower Camera, not as responsive or fast shooting as the 5DIII - you can feel the much bigger file sizes.
Lightroom is much slower in generating previews, making adjustment etc. that will many be fixed, but I am thinking about a new computer (currently using MacMini3GH i7 and 16GB Ram)
New great feature, a leveling arrow in the finder is great and sensitive - this is really great.
All in all a great camera as the 5DIII with much better image quality - I have on order, and the rumors tells me that Canon ship on June 16 in my Country (Europe)
Cheers, TES