First off, if you're planning on building in a few months, then you may as well wait for the Bulldozer release. It's unlikely that it'll match Intel's performance, but prices may adjust and there are rumors of new CPUs being released around the Bulldozer launch.
That aside, the i5-2500K is the right direction and what we'd all recommend for gaming.
With a budget of $1500, I can't imagine why you wouldn't go with the GTX 580, and you might have money left over to put toward the second one. At 1920x1080, the 580 is the best single card option, and since you plan on going SLI, you'd be better off SLI-ing the best cards rather than middle range ones.
I'd get the standard 1.5GB VRAM vs 3GB VRAM model, since the extra VRAM really only helps with multiple display setups (NVidia Surround).
flashing the 6950 is now pretty unreliable. And of course if something goes wrong, the manufacturer most likely won't replace the card. 6950 would be better for higher resolutions, as it has 2 gb of vram, so if you plan on getting more monitors it would be a better choice
If you're at 1920x1200, get a better card than the 6950. It does well in terms of price vs performance at that resolution, but the 570 > 6950 at this resolution. If it were a choice between 6950s and 560Tis, I'd vote for the 6950s in that case.
The only real advantage of the 6950s is the additional VRAM with the 2GB model for multiple displays, but since you're not planning on it, it doesn't make much sense.
Also, note that in order to play blu-ray movies (if that's what you intend to do), you'll need playback software. I've used Cyberlink's PowerDVD 10 Ultra and it was great - it has a good interface and was easy to pick up from the start.