Is there a difference between the 5K80 at $250 and the 80GN at $202 that would be important to running on an empeg?
Nope. I think the 5K80 is 5400 RPM (vice 80GN's 4200 RPM). On the empeg, a 5400 RPM or faster drive won't help you out at all, and will just create more heat and noise.
Incidentally, Googlegear has changed their name to ZipZoomFly due to a
lawsuit from Google. The lawsuit makes Googlegear look pretty stupid, and if you look at the "About Us" page on ZipZoomFly, they're pretty much lying about why they changed the name. But as long as I get my drive in good condition I'll be happy. They've always had good reseller ratings.