Lol. 800W? Seriously? I run an overclocked HD6990 from XFX with a GX750W from Cooler Master. Works with no problems. Don't waste your money on PSU. get what you need, not whats the best out there. Besides, in a few years you're probably going to scrap your current PSU and get a new one, so why waste your money?
Also, if you aren't on a strict budget, getting a Earthwatts 650W PSU by Antec should lower your expenditure in that area, which gives you a chance at getting a better case. i recommend the HAF922. I use it, and believe me, the 200mm fans and the option for 2 x 120mm fans on the side does the trick
. No worries for airflow. If you are not able to get the HAF922, then go for at least a Coolermaster CM690. it has adequate airflow for your GPU.
I assume you are not putting your Case out in the sun, as that would be ridiculous anyway. Honestly, don't worry about airflow too much, the 560s will not generate as much heat as the HD6990. Even then my HD6990 does not go over 60 celcius in the summer.