If you were looking to upgrade from a 4850, with a budget of $250-300, would you wait?
I'm also playing a similar waiting game. Picked up dual HD4850s (512mb) for crossfire just over 3 years ago when they launched. Bought a 1920x1200 monitor and everything was peachy. Then, in 2010, I picked up a 2560x1600 display. Ever since gaming has been bordering on painful (and I often end up playing at none native resolutions as a result). Came really close to upgrading to dual HD6950s when on sale, but it didn't end up working out (only got one of the cards delivered when I had ordered 2, so I returned the first).
The thing that has really kept me waiting is that I want to get away from crossfire if possible and the HD6900 series just wasn't quite there in terms of performance. If you upgrade your graphics cards every year or two, I think crossfire can offer great performance value. However, with my Visiontek HD4850s, after a certain driver release (somewhere before Cat 10.5) crossfire just stopped working in most games. Getting a 3rd party bios from a more recent HD4850 card largely fixed this, but this is not the sort of thing you should be expected to do to make your graphics cards function properly for more than two years after purchasing. It took me a long time to find the solution and I could have risked damaging the cards. Then there are all the other little image quality niggles that sometimes crop up with crossfire.
The HD7970 (or whatever) can't come soon enough as far as I'm concerned.