I don't tend to force anything and previously just left the 3D settings as the default NVidia setup, but this caused playback problems after about an hour.
Playback performance is better if I let the 3D application decide and constant reboots are not necessary. I don't think my particular situation is helped by using an NForce 630a motherboard which has very poor NVidia driver support/compatibility.
The main thing is playback is now sorted and I can enjoy superior PQ
