1. X700 128mb £69
2. X700 256mb £75
what is the difference? And is the X700 a good card?
X700 is an OK card and will play all the latest games (sometimes needing low settings though).
I doubt the 256MB will make much difference (5-10% at best in RARE occasions). I Would say it's likely not worth the £6 extra, get an old game like UT2K4 or FartCry with the difference instead (not sure if your prices are as good in the UK for old games).