The difficulty of 2xBW depends a lot on the bodyweight. I'd definitely believe a lightweight guy could pull 300-350 with only general strengthening and a little technical practice. I don't remember exact numbers, but I lifted close to 1.5xBW the first time I really tried, and I hadn't done any serious leg or back work before then. That jives with what was said earlier in the thread.
I'd be surprised if kettlebells (or light fast pulls) alone could reliably get the average person over 500.
"The enlightened never cease forging themselves."
-- Morihei Ueshiba