AGP to PCI-E card - upgrade advice?

Hi tech experts and eye-candy geeks…

I’m in the lucky position of having a Intel Core 2 Duo E6300 and a ASRock 775- Dual-VSTA Motherboard with 2 GPU slots (1x AGP and 1 x PCI-E) donated to me - so I can finally go dual-core and go to PCI-E and bin my old PIV and 6800GT and join the 21st Century.:banana:

I’m planning on sticking 4GB of RAM in there (Crysis + FSX here I come!) but am looking for a new graphics card to give me a boost from the 256Mb 6800GT.

My preference is for Nvidia (just had no problems with them - so I’d like to stay that way) and budget is roughly £150-200 smackers (depending on if Mrs Flash finds out…;))

Any suggestions? Some of the gaming mags say the 512mb 8800GTX gives best bang for buck?

Or should I go for a 9800 series card?

And anyone in London/UK cheapest/best place for cards? (dabs? yoyo tech? computer exchange?)