Gurm I'll take a look later at the Radeon drivers for any hidden settings or if the DP_DisableDither
keys have been renamed, etc.
I've seen some things relevant to the NVidia Windows driver and dithering but I doubt it's going to help us because the supposed 10xx dithering happens even with the Linux driver or even just a generic framebuffer, which in the case of the former dithering settings are exposed in the NVidia control panel but seem to have no effect.