ATM, the best you can use is the Raytrace Viewer that can be set for auto if you wish.  I find that annoying when used in the Material Room so I would suggest leaving that feature off.  It does have a refresh button and, as I mentioned, is very convenient in the Material Room.  Just have your render settings at default and don't attempt to preview with a final render setting.  It will completely bog down your app.

As for the PrincipledBsdf node, that is only found in P12.  I have been using it exclusively for Superfly Cycles materials and renders, it's much more robust than the PhysicalSurface node and you can connect more than one to Mix Closure nodes for more elaborate materials.