I decided after much thought to upgrade by 35L I to the 35L II - I traded / sold a few lenses to do it (35L I, 50L 1.2 and 200 F2.8)
I am a 5DSR owner and I have been trying to figure out a lens strategy for this camera that gives me the results that I want hand holding the camera. As such, from a wedding lens perspective, this has meant using the camera with only IS lenses (Canon 70-200 F2.8 IS II, Sigma 24-105 F4 OS, and Canon 35F2)
I have moved using my long fast primes (85L and 135L) over to my Sony A7Rii because of IBIS and the ability to use much lower SS.
Picked up the 35L II today - all I can say is wow - I will say it again wow. 1/125, F1.4 on any AF point on the 5DSR and it is sharp - really sharp @ F1.4!
This may just be the lens that makes me try using a 35mm Prime instead of the 24-70 F2.8 II.
It is so much sharper than the 35L I it is crazy - and that was a lens that lived on my 5D3 during lower light situations.
I cannot possibly recommend this lens more highly.
I read the reviews and was so anxious to see the results - it is even better than the reviews say (especially on the 5DSR).
This lens' reviews were the reason I decided to part with my 50L - because you can see what will be coming in the next 2-3 years as Canon updates the 50, 85, 135 with newer technology.
If you have the means, go buy this lens