I'm prepairing the results to upload them, but here are my first impressions:
UHD works great, no flicker at all in my test, BUT I noticed a serious increase in render times, so it went from 46 secs per frame to 1 minute 4 secs per frame, this does 20 seconds more, I'm not sure if this is just due to precomputation time or due to render time, in this case precomp time for the last frame was 39 seconds while render time was 19 seconds (plus other things like parsing and Geometry it is 1 minute 4 seconds) so maybe is due to precomp time.
Cheers!
P.S.: BTW what is the surprise? :)
EDIT: Another thing I notice is more noise :S