Ok, Thanks guys, I've ordered a Sapphire HD4870 just now. The mobo supports Crossfire so all should be easy!
my recomendation to u would be to run 2 4870s in x-fire as the sapphire is a very good card with more overclocking powers both in the clock speed and memory, also has fan enable, and the auto clock in cataylest works very well. I know iv made that mistake myself, but once u have ati cataylist center working good with both cards at the same specs ull be one happy gamer, everyone says u can run this or that, and that may be so, but do it right or ull end up nmot quite as happy. besides the sapphire 4870 is an exelant choice and one more is good because the price is down, go for it.