Honestly I would not use discogs as a source for covers unless you have no other choice. Their 600px restriction and -as you said- fairly unsorted way of storing the images is hardly useful in my opinion.
Personally I use this site to search for covers and I've integrated it into my mp3tag workflow with a tool that I've written. Usually doesn't take me more than a couple of seconds to find a sharp 1400px album cover that way.