No. I'm using iMac late 2013 (with Clover).
As far as I know, EA244uhd is a typical MST display. I wasn't sure if what my monitors shows in the menu (3840 x 2160 @ 60Hz) is really true. But interface operations, mouse cursor movement are absolutely smooth. Ocean Wave benchmark shows something like ~59... fps (almost 60).
It means one of these two options:
1) depending on MST implementation, MST may or may not work with NVidia or stock drivers;
2) EA244uhd uses SST.
By the way, Anand says that EA244uhd uses MST:
"One difference with the NEC EA244UHD compared to other UHD monitors so far is that it defaults to MST being enabled for DisplayPort 1.2"
Read just below that--it uses SST whenever it detects a problem with MST. You do not have working MST in 10.9.5.
Great to hear Rominator!