The best one I found was this one. Capable of 2k@120hz. The problem is that most dummy plugs out there are HDMI 1.3 or DP1.2. I have been in contact with the manufacturer to see if it's possible to edit the EDID of the dummy plug, and they said it wasn't, but they were working on higher end dummy plugs.

This was a while ago, and I've since moved on from my VFIO setup, so I never explored this further.