Still no fix from the makers although they are still looking at it.
I just reflashed my box with current OpenATV 6.4 nightly, and obviously the juddery playback returned as expected, but I did discover something.
I have the ServiceApp plugin installed, which adds two extra services for playing back streams with gstplayer and exteplayer3, handy if you use IPTV like I do, for troublesome streams. So now we have 4 services for playback.
dvb - 1
iptv - 4097
gstplayer - 5001
exteplayer - 5002
The default media player in ATV is called EMC (enhanced media centre) and when you list your recordings you normally press OK to watch one. Cue juddery playback....
If you press the stop button instead a sub-menu pops up allowing you to play the recording with "Service ExtEpPlayer3" or "ServiceGstPlayer".
Playing back with either of these services is judder free. Also is more responsive when you skip through the recording with the number buttons (like the old drivers are).
So a workaround not a solution, but for those who NEED the latest drivers because of all the other bugs they've fixed since they broke playback, you can use OpenATV, install ServiceApp, and play with either of the new services by pressing the stop button when selecting the recording.