Did you change the image resolution?Doesn't work. I already tried that way back (when they introduced the feature actually).
So unless they changed the way cover art displays I don't see it doing anything (if they did change it please, tell me so I can re-do the changes on my images)
I changed all of mine to something like 200x200 for square boxarts and whatever the equivalent is for letterbox ones (200x160 I think) and I no longer have any stutters.