Upgrade suggestions 8800GT

Hi,

I'm a little outdated when it comes to the pc grapics card market as I have not been playing for a while, but with some new games out there i'm looking to upgrade the graphics card. I've just bought Battlefield Bad Compay 2 and its running ok at 1680x1080 but it seems to be struggling at medium settings.

My system is as follows:

AMD 64 x2 6000+
2 gig ddr2-6400
8800GT 512mb
ASUS M2A-VM

With so much choice out there in the graphics card market im looking for some advice on what to upgrade to. Im not looking to go SLI/Crossfire but would like to spend about £150 on a new card. I have done a little reading but I would really value some input as to what to get as I dont even know if NVIDIA or ATI is the way to go.

Could you please add some suggestions as what would be a worthwhile upgrade for run games at 1680x1080

looking at the prices of the cards the GTS 250 is under budget but is this a worthwhile upgrade? (£100)

On the other hand the HD5770 is just about in budget at £150 (is this worth the extra cash)

Thanks for reading