It depends. The cards are actually fairly equal, as long as they are the same type of cards. As you already stated, the 9250 has an extra 128MBs of ram. (truth is, this doesn't matter to much.) If you can, look up the model numbers. Your looking for the clock speeds, both core and memory. (some 9250s are clocked 240/400, while others are clocked 240/333) You also want to pick the card with the better/higher bit bus memory. If one of the cards has a 128bit memory bus, and the other is only 64, then you want the one at 128.
Another thing to consider. You already own both cards. Download and install fraps and do some testing of your own.
Forgot to mention something. This forum is overloaded with babies who feel better about themselves if they call other people names. Ignore them, they aren't worth even thinking about. As my debate instructor said, "he who resorts to namecalling first, has the weaker argument." In this case, I'd change it to "he who resorts to namecalling is a loser who shouldn't be dealt with." I also like the ebay idea. Even a 9550/9600 will be faster then either of these cards.