I think I would get the 800 just to be on the safe side. And I would suggest that you get one with the L1 bridges NOT intact. I suggest this is better because you will be getting a more recently manufactured chip, which may be more overclockable. Just don't get one so recent that the multiplier is locked via the "missing pins" trick.
From a larger perspective, is there a significant benefit to extreme cooling with an Athlon, given that the multiplier is adjustable? Can it really have that much effect?