I was able to A/B the microRendu V1.3 against the ultraRendu. Then I sent my microRendu 1.3 in for the upgrade to 1.4 status - all the while I had the ultraRendu on loan. Then I had a brief audition of the ultra vs the new upgraded microRendu - but with only about 10 hrs on the new microRendu.
To my ears the ultraRendu was a clear step up from the original microRendu. Made the micro sound white-washed and tizzy in comparison. More "meat on the bones" of instruments, as well as better more solid instrumental delineation, and an expanded soundstage. Better everything.
The version 1.4 microRendu (same board as original microRendu, but with the same clock as the ultra) definitely occupies a middle ground between the original micro and the ultra. It had a lot more meat on the bones and not tizzy anymore. But, instruments were a bit "hard" sounding in comparison and not as natural. The soundstage also wasn't quite as extended. Ultra is just that bit more relaxed and natural sounding in comparison, but the 1.4 does get much closer to the mark.
I ultimately wanted that extra refinement with the ultra, and cut someone a very good deal for my 1.4 micro to help finance the jump to ultra.