IMHO spending £200 on an overclocked HD4870 512mb is waste of money!! If you want to spend £200 buy the cheapest GTX260 216 shader version as this is quicker than the HD4870 in most games.
The 30mhz overclock of the overclocked HD4870 can be done with a cheaper HD4870 512mb using ATI Overdrive,Rivatuner or ATItool. I have done this with every desktop graphics card I have bought in the last 5 years.
Also the problem is that with newer games like Crysis Warhead and Farcry 2 the 1gb HD4870 is faster than the 512MB version especially with AA:
http://www.guru3d.com/article/amd-at...024mb-review/8
http://www.bit-tech.net/hardware/gra...olden-sample/4
http://techreport.com/articles.x/15651/9
This is only at 1680x1050 too!!
If you are running dual monitors you are having an effective resolution of 2560x1024 if you span a game accross both of them!!