I'm not sure too many people are going to be able to give you a great recommendation, especially without knowing what you're using your machine for. Do you do image work? You might be interested in an IPS panel monitor instead of a cheaper TN panel. Keep in mind, they get pricey when it comes to IPS panels.
Personally, I use an Acer B286HK, which is a cheaper, TN panel Ultra HD monitor, and I love it. It has a USB 3.0 Hub, height adjust, swivel, tilt, and works wonderfully in OS X, but it has a few trade-offs that might make it less desirable for something as "Workstation Grade" as you might be looking for. For example, my particular monitor has some heavy back light bleed when looking at blacks and dark colours, and the colour accuracy isn't as spot on as the IPS panel I have sitting next to it, but that's why it's sitting there.
In the "Peripherals" section of these forums, there are extensive discussions on 4K and Ultra HD monitors and Macs in general; there might be existing information there to take a peek at. It seems to me though that you have enough graphics horsepower to power 3x4K displays, or whatever you choose to go with.
Hope this helps.
-N