One of our engineers recently visited a site that had a new Mac Pro that was under performing with significant lag when using any of the photoshop tools or even zooming in and panning around the document.
Opening the same file on an identical mac did not reproduce the problem, the only difference was the problem Mac was running 10.11.5 (El Capitan) whilst the other was running 10.10.5 (Yosemite).
He checked all the usuals – the disk was healthy, Photoshop and Mac OS were patched and all the photoshop settings were exactly the same as the working mac….with the exception of “30 bit Display” this was greyed out on the 10.10.5 mac, but live and ticked on the 10.11.5 Mac. He unticked this and immediately the performance matched that of the working Mac.
Upon further reading it appears that Adobe quietly introduced 10 bit colour in PhotoshopCC 2015, but Mac OS 10.11 is required. The Preference can be found here:
Photoshop > Preferences > Performance > Graphics Acceleration.
You can find more information here.