Jason is correct, the zoom head does add a lot to the flashes capability. A few more features I like about the 800 & 900 over the 600 are 1) PC cord connection for use with pocket wizards without a hot shoe adapter, 2) High voltage input for use with Quantum style packs, 3) Commander mode for 3 TTL flash groups, and 4) the envy of every Tim Allen fan "More Power! And if you have now read it yet, get "The Hot Shoe Diaries" bt Joe McNally referenced in Jasons post. Not only is there a wealth of info in it, he's a very entertaining writer. My wife calls his style of writing "Stand up comedy for Photographers". It's well worth the investment, you will want your own copy.