Yea I know the 7850 can run BF3 on ultra at 1440x900. The 6870 can at 1280x1024 cause my friend has his set to that. The 7770 OC'd can supposedly max BF3 to cause I have seen a lot of things on it. I can OC my current card to 78GB/s easy(its stock 57.6 right now) which is the bandwidth for the 7770. Only real problem I am having in getting the 7770 is the 128-bit with CF where as my curret card is 256-bit and can OC pretty freakin high do to that. I can hit about 90+ max with my card OC'd till I get a blue screen.
Another cnsideration for you, specially if your thinking of CF the two 7770's, is microstutterig. On all low to midrange cards, the phenomenon is particularly bad. And can really take the pleasure away from gaming. Do a search on Toms an you will find a interesting article. The upshot being that the best advice is always to go for the best single card setup that you can afford. On that basis, I would avdvise to wait for the 7850, or when you can afford something comparable!