I don't believe the evga made a 5600 256mb. As far as I know, BFG was the only one to produce the 5600 256mb.. they called it the "Asylum". I know, because I have it.
I just purchased a new 6600 gt because my 5600 is not giving me the performance I want. It will definitely play the newer games but it lags a lot when at higher settings.