Hehe, I didn't notice any lagging when I used them for a playthrough, so I figured they should be ok at that size.
If anyone has any problems they can always resize them themselves.
The animation is partially related to the file size, as instead of having it at say 512x512 I had to double either the length or the width so as to fit the second frame of the animation on.
If i'd wanted to make it reeeeeally detailed, I could have gone further and added more frames, but that
would have been taking the piss somewhat, I feel.