A ringed WD I haven't found yet and suspect I would only find one in a higher code system,perhaps part of a neutron star/black hole system.
Don't recall seeing one in a neutron star system, but I've seen a handful in black hole systems. I think you're right though, probably at least mass code f if not g/h. Which reminds me of this find nearly a year ago...

The ring around the WD is pretty huge, and if there was less water in the atmosphere I reckon that'd have been a good candidate for a possible ELW... Might pay it another visit soon, don't think it's too far from Colonia and my first visit was before they updated WDs with jet cones...