Hi all. (especially Zing

)
I need to replace my ageing (and failing) NvIdia 7900GS card.
I was looking at an 1GB ATI 5770 for around £100, but have just seen a 512mb ATI 4850 for about £50 - so which would you recommend i get?
Mainly play a few games like MW2 - which runs fine, although my card is failing so i get lots of artifacts once it warms up. I also have battlefield BC2, which only runs at a rubbish res of around 800x600, and lags like hell.... as such i've only played it for about 10 minutes in the last month!
So of the 2 options above, which would be better value, and would both cards run both games on a 22" tft at a fairly decent level?
TIA