OK, here are two screenshots of how it looks like on both the Touch and the Paperwhite using 50x50 images. I simply took your images and scaled them up, so it's not terribly good quality. But other than that, I guess that should do, so natively using 50x50 (or maybe 48x48) should be ok.
One more thing: if you take a careful look at the KT screenshot, you'll see that the "trash" icon seems to have the lowest one or two pixels cut off, so it looks slightly asymmetric. I don't know what causes this, but I guess the easiest solution is to simply use 48x48 / 46x46 images with a 1 or 2px (transparent) border on each side.
So... what do the other people here think?
Last edited by ixtab; 12-19-2012 at 07:56 PM.