Well according to the tomshardware review it is not worth the extra cash.
http://www6.tomshardware.com/graphic...604/index.html They said it barley get's any more FPS within 10 I think at the highest resolutions then the 128meg version. They also said the 256 meg version is using the DDR2 mem which they said runs very hot. If the review is correct just go with the 128meg version save some cash and unwanted heat.