I had try 3K r3d files with VP9 / core2qud Q6600 / 3GoRAM : changing the preview setup to "sharp/quarter" allowed me to playback at full frame rate (with no effects on event !) and good image quality in the preview window (despite "sharp/quarter" !!! because there are really a lot of pixels).
But time render was huge (30s r"D 3K -> full HD Sony AVC takes 5 minutes !!!)