"Computational errors, no matter how rare, are unacceptable", but no ECC RAM? I think halve of the memory, but a XEON with bigger cache would be the better choice here.
And Chenbro has some nice cases, like the SR20968.
-i put in a much more powerful video card given a 6450 from what i know wont drive 2 1440p panels very well. the gtx 660 can be used for CUDA applications if need be
-no guarantees this stuff will work with fedora. id be safe and go windows
-chose a silent case. should be pretty easy to build in
if you make money on this machine, you would want the most performance you can get as time does = money.
you can check out this review where they show the newer 3970x (3930k can be overclocked to same levels) against the 8 core e5 2687w (basically a e5 2650 thats overclocked 1ghz faster). the difference between the 2 are 5-10 sec. the differences are noticeable if you do a lot of work.
you should overclock the 3930k if you are going to get one. 4ghz is perfectly stable and achieveable