Thats a difficult choice ,if you buy one you might later wish you had bought the other ,the 577 maybe being the more usable[lighter weight] ,the 600 being ,you only live once ,so take the 600 ! There is a photo of a 10 bore double rifle owned by one of the Nizam of Hyperadad in Graham Wrights 2nd Edition ,thats an interesting story about the last Nizam who bought a sheep farm near Perth, was bad at managing money, drove like a maniac ,was constantly being sued by parasites ,lost all his wealth and was a book written about him !