In a choice between those two, the UR22 wins!
You may think that because you are only using midi that an audio interface is not necessary. This is a common misconception. The audio interface provides an ASIO driver and will work much better because while you may only be playing or recording midi, your VST instruments are not midi, they are audio, they output audio from midi, if you use a keyboard the ASIO driver will get you better, lower and more stable latency, even if you are just playing back midi notes through VST instruments, the whole thing is going to be better with the UR22.
In terms of processing power, this is not really relevant given the beast of a machine you have, there is unlikely to be any difference there. In terms of sound, you will get better clarity from the UR22 and better stereo placement, plus the convenience of real knobs to turn.