This PSU (Hcg900) http://www.newegg.com/Product/Product.aspx?Item=N82E168... has 150 more watts than the tx v2, is slightly better quality for $10 more.. CFing with the 6950 takes around 510~ watts, so 750 isn't cutting it that close, but with overclocking / larger gpu's in the future you may well be.
for the case i would say take an Antec or Coolermaster , keep in mind that those full tower cases can be quite expensive/ large on the opposite site , those big cases will most likely provide enough cooling and have enough space for adding some more hardware in the future
All the aforementioned cases have superior cooling. The haf 922 probably has the best considering its large fans and roominess. I am very pleased with my antec illusion, as I got it for $55 and it comes with 4 fans. I also appreciate its plain black look (i snipped the LEDs). Im not positive about the challenger, but the other 3 will definitely fit those components. Below is a rather amusing shot of a packed antec illusion. It has dual 6950's, and a massive scythe mugen cpu cooler: http://www.tomshardware.com/reviews/intel-sandy-bridge-...
Based on current prices, my top choice would be the haf 922 if you dont care about aesthetics. Not only is it the best of the bunch, you really cant do much better for any price in terms of functionality.
That being said, an antec 300 illusion with a scythe mugen will give you lower cpu temps than a haf 922 with a hyper 212, so you gotta make sure youre putting your money in the right place if youre squeezed.
I need to total everything out but I will more than likely end up with the Antec and a scythe. It seems to be the best value and correct me if I'm wrong but I could add the scythe at a later date if th current budget didn't allow it.
Also a side note, the asthetics won't matter if your gpu melts.