I have a layout which mimics the game launcher front end, which stretches the snapshot full screen behind the text list. There's a place in the settings where you can disable updates of certain front end drawings until a user defined delay has been reached. I've found that I have to disable snapshot real time update, and utilize the delay, or scrolling is super slow. Have you unchecked snap on that menu?
This delay that I speak of, also affects the settings you place in the polling settings, or the two settings fight and make it slow again.
I've experience similar frustration, but I now have it where the joysticks seem to scroll adequately without updating snaps, trackball works, but not half as well, and the spinner works also, slightly better then the trackball.
I'm personally a bit disppointed in this area myself, but haven't exhausted searches or combinations to try to help the matter. I might try down-resing my layout smaller then 1200x1600 and see if artwork updates faster (I have an LCD, so I'm kinda stuck with that res..)
If this helps, great. If not, then I feel ya.
-csa