Alan, I think my opinion is biased towards 1080i as I have a 1080P set where the video processor in the TV apparantly holds the alternating 540 lines at 60fps and displays them as 1080P @ 30fps.

All I know is if I set my STB or Panasonic upconverting DVD player to 720P it looks more jaggy than if I set it to 1080i. I think its because the processor has to do more converting. Does that sound like a correct assumption?