hd 5670 is better than both 9600gt and gt240 by 15-20% in most games, so if you want performance and dx11 5670 is the best choice at the same price of 9600gt-gt240.
just checked and he is right, but its more like 10-15%. crysis is 1 of the games where the 9600gt beats it. the 9600gt beats the gt240 in pretty much all of the games. so u could get the 5670 for the dx11 and slightly better performance but u would lose out on phsyx. according to rumours, the lower end cards in the 400 series will be releasing in the next few months so you could wait.