For standard definition viewed on 768p panels, the best option may well be to send 480p to the display, taking advantage of the excellent deinterlacing capability of the ABT chip, but thereby ensuring that the image is only scaled once. I've never understood why it's often recommended to send 720p signals to a 768p panel (as it's "closest" to the native resolution) since that necessitates 2 scaling operations (480p to 720p in the source device or AVR/processor, then 720p to 768p in the display). Each scaling operation can only degrade rather than improve the image.

Of course, that assumes that the panel has a good scaler, but many do. It's certainly worth trying 480p.