I have that RAM, works great with my i7 930 on that motherboard with that GPU...you pretty much picked out my build except I got a Diamond Radeon HD 5870 and an Antec case and PSU. That RAM works great and is easily set to 1600MHz full speed on that motherboard (it isn't detected properly, defaults to 1066MHz but with a simple tweak in the BIOS it runs at 1600 just fine). It can handle higher voltages too, rated at 1.65V but works fine around 1.6 or less usually. Mine is overclocked to 1720MHz with my i7 running at 4.1GHz so that motherboard/CPU/RAM combination can definitely overclock if you have proper cooling. I'm using a Corsair H50 but any good air or water CPU cooler should give you a 4.0 or higher overclock. The stock heatsink you can probably hit 3.25GHz without too much heat but that's about the limit of the stock cooler.
As for the case, the biggest thing I'd worry about is the 5870. The 5870 is a monsterous card, huge doesn't really even describe it, the thing is ridiculous. It's not as big as the 5970 but it is approximately 11 inches long (if you have a standard keyboard think about the main block of keys, it is about that size). It fits in my Antec 900 with less than an inch of clearance and I'm pretty sure that I can't use the drive bay behind it because it is blocked by the back of the 5870.
Do you plan on buying a hard drive? I don't see one listed in your build. While it isn't a critical gaming component you should at least choose a decent one. If you have money to burn you could get a solid state drive (or several of them to make a decently sized RAID drive) but since they cost over $100 for 64GB I don't recommend them unless load time is critical. I have a WD Caviar Black 640GB in my desktop and the load times are pretty good, it loads games and apps fast enough that it isn't annoying. My friend opted to save some money on his build (almost the same as mine, same case/GPU/CPU/RAM/PSU) and he bought a WD Caviar Green 500GB. The difference is quite noticeable as his takes a long time to boot up. A 7200RPM drive with a good amount of cache (32 or 64MB) is recommended for your boot drive. Storage drives generally will be fine with 5400RPM as they aren't used as much and seek time is usually less important (storage drives are more commonly accessed linearly than randomly while boot drives are accessed very randomly and seek is huge).
