I guess this is a more generic question than Rhino 6 related. The difference between professional video card and gaming one is in the stability of the silicon process and the QA. In layman terms it means that professional video cards are more reliable for prolonged use, while consumer card (on average) tends to break earlier. Moreover NVIDIA offers more stable drivers with less cutting edge features but that do not crash (they do but less often) and VRAM with error correction and some goodies.
In short, if you need a machine with more video RAM and that you plan to have for severl years and you need to depend on go with professional cards, if you think you can survive with some crash and chaning the card every once in a while, consumer card are the one you want.