My wife purchased a Retina MacBook Pro last year around February. We are looking for the best 4K monitor to use. Unfortunately, it's a little confusing researching things between single-stream and multi-stream. Does a multi-stream monitor require 2 Thunderbolt/Mini DisplayPort cables to operate? When monitors include USB ports, do you also have to run a USB cable to the monitor in order to use the monitor's USB ports or will data transmit over the DiplayPort/Thunderbolt cable? What monitors do you guys recommend that will work the best with a rMBP 15"? I've looked at the Dell UP3216Q, Dell P2715Q, and an LG MU-3197B and MU-3197Z (Thunderbolt) monitors. Any thoughts?