Ring of Kings is pretty rare, like a 1 in 100 chance of any particular ring you find being one. It'd be neat to see two of them on one guy! Even then, the benefit might not be worth the trouble once you get up in the higher ranks
That old FAQ Jim2wheels refers to is definitely a very good resource for now. Quite a few of our items don't exist in that old version, and even some of our monsters are different, but it is still good reading for anyone who wants juicy details. We really need to get one done here of that caliber but I can't even find the time to finish the 1.6 update yet!