Roger Cicala didn't wait long -- he just published imatest numbers for 3 high quality lenses and 1 average lens on the 5D3 vs. 5DS vs. 5DSr:
http://www.lensrentals.com/blog/2015/06/canon-5ds-and-5ds-r-initial-resolution-tests
Short answer: a rising tide lifts all boats. The lens doesn't need to be mind-blowingly good to benefit from the added resolution of the sensor in the center of the frame, but the average lens didn't resolve much better in the corners on the new rigs (which we might expect).
Anyway, give it a look when you have a moment.
- A
http://www.lensrentals.com/blog/2015/06/canon-5ds-and-5ds-r-initial-resolution-tests
Short answer: a rising tide lifts all boats. The lens doesn't need to be mind-blowingly good to benefit from the added resolution of the sensor in the center of the frame, but the average lens didn't resolve much better in the corners on the new rigs (which we might expect).
Anyway, give it a look when you have a moment.
- A