On Apple's 5k iMac spec sheet, it says it supports an external display up to 4k. Previous imacs could run 2 external displays up to 2560x1600. Can anyone with a retina iMac test two external displays and see if it works? My theory is based around the number of display port channels on the graphics card. 4k externally requires 2 display port streams. If they are using 2 streams internally, overclocked, with the custom Tcon, and 2 externally, that gives four. Normal displayport displays ( up to 2560x1600) use a single stream. Therefore two non 4k displays should be doable. Thoughts?