Originally posted by Winning
IMO AMD's aren't great.
I like AMD just as much as I like Intel. Nothing's perfect, and it all depends on what I have to spend. :p I would take a 2500K over my Phenom II 970 X4 any day, though. =D
In regards to OP:
If you want to use CrossFire, stick with the 6870. If not, go for a 5870. Your motherboard won't be able to utilize CrossFire anyways, so unless you want to upgrade it in the near future, go for a 5870. They're better single cards, 6870s are better dual cards.
As for the CPU, if you have a little extra money, you could get an AMD Phenom II X6 1100T, it performs better and isn't too much higher in price (forty or fifty USD, dunno what that is in your currency. Dx).
Upgrade to 8GB of RAM as well, when you can. Not right away, of course, but you might as well use your mobo to the fullest.