UPDATE - 10.10.3 brought 5k support for OSX, but I no longer have the UP27 -------------- I know there is a mega thread, but I get lost in there - I'll keep my conclusions simple. We are running 2 UP27 and 1 P27 off a nMP (d700) with no issues. The UP27 does show pre OS screens (alt boot, etc) while the P27 does not. OSX - the P27 is noticeably clearer than the UP27 at any resolution. The P27 is a little soft due to the AG coating, but the UP27 fuzziness is worse. At 4k, the difference is less noticeable but still present. Note, I could not get 5k from the UP27, so if you're only working in OSX, then there is no reason to get the UP27 over the P27 except the caveat about no pre OS screens. WIN - the UP27 at 5k is razor sharp, and the P27 at 4k is very very close (even with the AG coating). Note, install the updated AMD drivers for boot camp http://support.amd.com/en-us/download/desktop/bootcamp The P27 is $500, the UP27 is $2500 so would pick P27 over the UP27 for every application since it is a LOT cheaper, noticeably clearly in OSX and almost as good in WIN. It would be even better if/when the P27 gets support for pre OS screens.