The PSU is good enough.
Not sure if you actually checked, but the C43 does not support crossfire or SLI.
You should be using 2x2GB or 2x4GB sets to take advantage of dual channel memory. It will work with just one stick, but 2 is twice as fast for memory access.
And of course with sandy bridge you should be using 1.5V memory.
Case is ok.
GPU is nice, and if you already got the parts then i guess you know if it fit or not in that case
If you don't have em yet, make sure it fits.