Hmm, Dual nVidia GTX 560 on an AMD motherboard ain't going to work. Everything else looks good. While you are putting it together fresh might I suggest you invest in a liquid cooler? A Corsair H80 or H100 will give you quite a bit of overclocking headroom (and quieter operation over an air cooler) and is much easier to install fresh since they require a backplate switch.
And you'd trust nVidia and AMD drivers to play nice with each other without issue? I wouldn't. But I do agree with Hardwood that a single more powerful card trumps two cards of equal on paper performance, because you have drawbacks when you use multiple GPU's (microstuttering, non linear scaling, etc). I would say wait for the HD 8000 series as well, they're generation 2 Graphics Core Next which should boost game performance like gen 1 boosted GPGPU performance. The other components you can pick up now if you find them on a good holiday sale.