I've always felt (pure speculation, also) that the way their drop system is works is total-kills based on say, a server level. For instance, if something is a 1 in 1000 drop rate then every 1000th kill on that server (or however it's grouped up) drops the item. I've *always* had better luck for epic and rare drops during off hours and this is the best system I've seen proposed that fits with my experience. To that end, I definitely try and farm when the server is a dead zone