I have a 2013 MacPro with dual d500 GPU's and an Eizo CG277 Monitor...which is the pinnacle of graphic design monitors. I can't enable GPU performance?! Retina monitors do not have near the color accuracy of Eizos.
My Eizo connects via thunderbolt 2 and USB...both at the same time. The bandwidth is definitely sufficient.
It is ridiculous.... I have more than enough power, let me utilize it. Your requirements are not valid for professionals.

Please expand your list of GPU Performance systems beyond "Retina Monitors"