So the retina 5k iMac can only power its own 5k screen and 1 4k monitor at 60hz. I want to add a second monitor on at 60hz. I tried displaylink and it worked at 4k but only 30hz. They have a new model coming out I hear which will do 60hz. In the meantime, if I buy a thunderbolt 4k monitor then will I be able to run both 4k monitors at 60hz and the built in one? Do I have any way to do it?