You have the advantage that when playing games that use alot of memory (which most new games do!) it is handy as it doesnt use as much system memory, however most 256mb graphics cards tend to have a slower clock frequency than their 128mb brothers.
However, for the price of a 256mb 9800Pro you would be better off getting something like a 9800XT 128mb or 9800AIW 128mb or a 6800 or 6600GT, less memory but considerably better performance, for either marginally more or the same price..
:good: