
SO, if I get the same performance from 970 mini and 460 4GB, and save $125 but have to bust out the back of Thunder2, Im busting it out. ASUS ROG STRIX Radeon RX 460 4GB OC Edition - 2.2 Tflops ( Amazon 126.99) (probably need power- probably not fit intoThunder2) GTX 970 mini - 3.5 tflops (250$ + power to Thunder2 needed) //////So it looks like to me safe options are: I rather spend a little more and be safe: So, the GTX 750 2GB is about the same performance as 460 2GB. I think he was thinking about the 2GB because I can’t imagine the 460 4GB having any trouble with 4K display. Troung (in an email he pointed me to ya'll), was concerned about the performance of 460. In general the RX 460 supports multiple outputs, so it should be able to drive both the BenQ and the Viewsonic (I assume OS X supports multiple displays, so that should not be an issue).
OS FOR MAC (27 INCH, LATE 2013) UPDATE
You might need to update your OS X to a newer version to get RX 460 support, and you will need the automate-eGPU.sh script, but I'll let the Mac crowd chime in to elaborate on this.

AMD RX 460 2GB: A version with no external power connector and one small enough to fit the Thunder2.Since you don't game I went for the simplest setup. If this is not an option: Your simplest (and pretty much cheapest) eGPU option to drive a 4K display. Just use a DisplayPort connection from said port to the 4K display. Does your system have a DisplayPort1.2 port in addition to the Thunderbolt1 ports? That would solve your quandary cheaper and faster.
