I have not been able to test this with a Mac Pro, but I do have a Macbook Pro. No apparent way to drive the monitor at 5K with dual displayport cables from a Macbook Pro. This is expected per the support documents. However, I'm pretty sure the Macbook Pro itself can handle a 5K desktop (it is possible to have a scaled 5K desktop output to a lower true resolution, so the graphics card is capable of it). It is possible to output at 4K and have the monitor scale it internally, so that's good. And it looks OK. What's not good is that the Mac seems to think the monitor's native resolution is 2560x1440. There is no combination of SwitchResX or built in support that will allow me to output at 4K with an effective scaled resolution of 2560x1440 in HiDPI, for instance. I have to output at 4K native, and as a result everything looks super tiny. Hopefully Apple will get their stuff together on this. In the mean time, I've been running it at 2560x1440, which is no better than my old Thunderbolt monitor.