Also, I wouldn't bother replacing that GTS 250 yet. Sure, it's not the most current VGA card, and it's not for playing at 2560x1600 resolutions or dual displays or whatever other crazy display set up someone wants to come up with, but the only things that really matter are what is your current display set up or are you planning on upgrading to something with more display real estate immediately.
If not, save your money AT LEAST until the Fermi based VGA cards come out in a month or so as it will change pricing on ATI's current premium 5XXX series cards.
Personally, I'd say wait until you upgrade your displays. The premium cards will be cheaper by then.