I am looking for a used F-200... First I was hesitant on getting one as I already own a very nice F-100 which overclocks nicely. How about you actually make a thread in the marketplace area. I would also recommend testing the clockspeed. How much can you crank the clock up? If it goes near 280 or even higher, you might want to ask for a little more then for a common unit as those are especially sought for by people.
Also: Make me an offer I can't refuse and I will buy it depending on where you are... I live in Germany so if you are in the UK that should not be a problem. I would buy one from the US aswell if the postage doesn't add too much to the price.