Upgrading from a 256MB 7600GT + Other questions

Hi folks,

My 7600GT is starting to get a bit outdated (been playing (or trying to play) games such as COD4, Fallout 3, Supreme Commander, and a few Steam engine games, and while my 7600GT suffices, i'd like to see what games are -supposed- to look like for once.

I've been doing some looking around, it seems that my best options are looking to be:

http://www.scan.co.uk/Products/1GB-XFX-HD5750-PCI-E-20%...
http://www.scan.co.uk/Products/1GB-XFX-Radeon-HD4650-PC...
http://www.scan.co.uk/Products/1GB-Asus-GTS-250-Dark-Kn...
http://www.scan.co.uk/Products/1Gb-Gigabyte-9600-GT-Mem...
http://www.scan.co.uk/Products/1GB-XFX-GT-240-1800MHz-G...

You might have guessed from the URL that i'm UK-based, so i'm looking for a UK supplier, and you may also have noticed that my maximum budget is around £120, give or take a bit.

I've been doing most of my shopping mostly by amount of video RAM (all of the above cards are 1GB models), but i've heard that it might be better to actually run with less RAM which is faster (say 512MB of DDR3), rather than more RAM which is slower (1024MB of DDR2) - what's the current thoughts on this?

Current specs:

XP SP3 (32 Bit)
IC2D 2.3GHz
450W Corsair PSU
2GB RAM
7600GT Fatality Edition

So my basic questions are - what should I be looking for in a mid-market card, in terms of memory bandwidth, clock, amount, etc, and whether anybody has any recommendations for something which'll last me a couple of years.

Thanks!