What to Upgrade? 120£ to spend

Be careful with ebay. I see alot of thing selling used at about the same prices you can get them new at a discount etailer.

What games are you playing?
What is your monitor resolution?
What FPS are you getting and with what settings?

Most of the 9800 series cards have 512MB RAM or less so you can get a good FPS boost just by turning Anti-Aliasing off and tweaking some of the game graphics settings to reduce memory usage.

Did you read the latest Tom's article on building a balanced system? Might be a good educational thing for you to look at.

Crysis is a monstrous game. It requires both alot of CPU power and GPU to play at the highest settings. Its really a quad core 3GHz, ATI 5850/GTX 285 kind of game. Look at the new article, it has Crysis frame rates with various GPUs and CPUs.

If you buying a second 9800, you may want to replace both with a DX11 card in a couple years. A 5770 will be about 50% faster than a 9800 but with DX11, the 5850 is faster than a pair of 9800s with DX11. Its a hard decision you'll have to judge for yourself. Getting your CPU up to 3GHz will help, but probably not as much as a boost in graphics power.

I did just trade my 9800 GTX+ for a 5770 and saw a significant increase in FPS in the MMORPGs I play. I can also play COD4:modern warfare demo with settings maxxed. My cpu is just an aging Athlon 64 x2 OCed at 3.2 GHz and I have a 22 inch 1380x1050 LCD.