If you are looking at cards in that price range, these are far better cards..
And also 512mb over 256mb really doesn't make that big of a difference.
And with your system it will make about no difference.
http://www.newegg.com/Product/Produc...82E16814102048
I have that card personally for now.
http://www.newegg.com/Product/Produc...82E16814102033
http://www.newegg.com/Product/Produc...82E16814102060