256mb was for 14k when i had went
a number of factors contibute performance of card,who says the core etc are most important.
Now,a 6600gt is not a very good card for the future anyways though you might benefit by 256mb in some games especially newer ones,be carefull if the card is slower as of now due to different ram.Also,what you can do is take 6600gt 128mb now for abt 10k
sell it after a yr for abt 4k
now had the 6600gt 256mb been for 4k,you
8k + invest some money
get better card