Does full screen display all the masters in 5K, that is Aperture gets the 5K rendering from the OS even if the app. isn’t updated?
Would slide shows created on Aperture on a 5K iMac, probably running El Capitan, be in the native resolution of the iMac? I know that screen savers are. I send iCloud photo streams to my Retina MacBook Pro from my regular iMac and it’s definitely sharper on the MacBook Pro than my iMac.
The latest 5K iMacs probably come with El Capitan.
There are reports that El Capitan supports 10-bit color but the app. itself must support it. For instance, Preview reportedly doesn’t support 10-bit color.