iPod Nano 4G Coverflow smoothness

I've just ordered my new iPod Nano 4G 16GB, and started filling my iTunes library album's covers to use the Cover Flow on the iPod. I just wondered if it can be a bit slower with all the album images than without them. I mean, is it reccomendable to get all the CD Covers on the tracks?
Also, the pictures of the albums I added are mostly 500x500 pixels, but some of them are bigger. Will they display correctly in my iPod?
Thanks!

have found that most pics are best at 150 x 150 resolution