Thanks for the compliment and for the speed tip on PAL. It seems like a simple and effective solution, although probably not always applicable. In my case, however, I'm not sure I want to give up the smoothness and regularity of the movement, especially when scrolling is involved. However, I will take this into account eventually for future games.
Yeah, before I implemented it I thought it would be noticeable, but it isn't, even when scrolling. It would seem the brain can't tell an object (or the screen) has moved twice as far in a frame, it just perceives the overall average speed.
Looks like you're scrolling a big area in this game though so I guess there might not be enough time to copy all the data.
Oh yes, in Tutankham's case it would not be possible for me to apply your "trick" due to the time used by scrolling.
Also, if a sprite moves exactly 1 pixel each frame (like carts or elevators in Bagman Comes Back), I can perceive a less smooth movement if every 6 frames the sprite moves instead of 2 pixels (I just tried).
In some situations, however, I may decide to apply your idea.
Thanks again.