Dan,
I did a test from a 720×486 uncompressed 8bit spot with these settings:
15 fps, keyframe every 24 frames, quality medium, audio at 48,000 size 640×480. There is a fair amount of pans which strobe slightly, but notably less with QT’s high quality turned on. (command J)
But I have a couple questions, why do you want this size? In what are you viewing it? QT? Browser? Does it flicker in all of those?