Hi Mike,
I don't know too much about the changes from the 2008 version, but I do know that we are constantly adding new material and tweaking the accuracy of our computerized tests. You'll get a fine study guide with our 2008 version (it's not like the GMAT has changed all that much in the intervening years) but you might still appreciate the newest refinements.
Kaplan 800 is just what it sounds like: a guide for test-takers really aiming for a top-tier score. I'd start with Premier to get the Kaplan methods down, then take a few practice tests before deciding if 800 was right for you.
Good luck with your studies, and let me know if there are any other questions I can answer!
Eli