5K iMac runs 30 fps only

Nope, runs at 60 fps.

Please, don't circulate BS. From Extreme Tech:

Updated November 4: Sadly, it’s time for a mea culpa. On October 24 we mistakenly identified the iMac with 5K Retina display as having a 30Hz panel. The 27-inch iMac does indeed output 5K @ 60Hz — and to hit those kinds of frequencies, Apple used its own customized timing controller, rather than DisplayPort 1.2 (which can’t drive 5K @ 60Hz). More on that can be found further down the story.

http://www.extremetech.com/gaming/192305-analyzing-the-imac-...

I was wondering about this after seeing the HN thread the other day about 4k screens and how the underlying response seemed to be "nothing is quite there... yet", and whether Apple would have cracked it with their new 5k iMac.

Looks like coldtea/extreme tech are right though.