I really don't know which graphics card to get anymore... Help?

The rest of my system is:
Antec 900 case
Corsair 750w TX
MSI K9A2 Platinum
AMD Phenom II 720 2.8Ghz @ 3.3Ghz
2x 2GB DDR2 800 RAM
2x 160GB HDD (Raid 0)
2x DVD+-RW

I had a HD4650 1gb but upgraded it to a 4870 1gb OCed edition, but i had to RMA it. At the moment I've gone back to using my 4650 but I don't know what to do about a replacement for my 4870.

I got a £127+standard delivery credit note from aria. I may be able to put that up to maybe £200, maybe. I was thinking a 5850 but I have no idea when they're coming and what spec they'll have when they do come (in comparison to my old 4870). Plus I checked Aria and already, they've got 2 versions of the 5850, one of which is overclocked to supposedly give 38% better performance, or maybe a 4890, and what about 2 4870s, quite often aria have discounts on 4870s, may even be able to get 2 of them if I look hard enough.

Oh, the credit note apparently lasts 6 months, so I can wait a short while till I get it, though I don't want to wait too long, my 4650 kinda struggles on Crysis Warhead...

Help?

Thankyou in advance..