My point was made, the iMac Retina cannot drive an external 4K (or 5K) display. It can only drive a standard resolution display. The Mac Pro can drive a 4K display using its Thunderbolt 2 ports, but the iMac retina cannot. A limitation of the iMac retina, in case someone would think it can do 4K external displays. It cannot even do Target Display Mode.
11/10/14 at 4:26pm