In a month or so we could know a little more about the release date for the new Radeon 7xxx series -- which may well happen sometime in Q4.
The dual-BIOS HD6950 is a great card, but you probably won't find a second card when you are ready with the new series so close to release; and the possibility exists the new releases will drive down the cost of cards like the HD6870 making an initial purchase of two cards a great deal.
And in the next month or so you should see some Bulldozer action from AMD.
Definitely recommend waiting till you have the money for your entire build before purchasing. Random parts by themselves do nothing... all that will happen by waiting will be more money saved by you.
I doubt MSY would price match (I know the one near me doesn't) But I rarely find they are more expensive than any competitor... remember too with purchasing online you have to factor in a shipping cost. Their range is not as good (No quality SSDs or gtx 560Tis) but even if you can get the majority of you gear from them you'll save... but wait till you have the money for your GPU... a month and a half can change things..