Here is the second dual E5-2670 machine I recently built (I made three in total, for three friends) (see the first one here). This rig features really compact size - the very popular NZXT S340 ATX mid tower, which is merely 38.4 liters.
The dual Xeon E5 motherboard I used, Gigabyte GA-7PESH1, is a large server board in SSI EEB form factor (12x13 in). Only a proportion of ATX full towers (typically 70+ liters) officially support such big boards. But S340, tiny but mighty, does the job well. I found this secret of S340 a while ago, and used this case for three of my dual Xeon builds (see my other work, caution: Chinese). It fits an SSI EEB board almost seamlessly, with just enough room in the front for water coolers (I put dual Corsair H60's in one build).
The most notable advantage of matching a server board with S340 is the optimal air flow direction. In contrast to consumer's motherboards, server boards are designed for extremely strong air flow in horizontal direction - it blows across the entire surface of the motherboard to cool down on-board chips, mosfets and other stuff. Consumer's cases are not typically designed for that purpose, but S340, with two giant 140mm fans blowing from right beside the board, meets this goal perfectly.
To install an SSI EEB board into a S340, you will have to deal with the three screw holes on the right edge of the motherboard. Apparently, S340 does not have these in its blueprint. My solution is to DIY an acrylic board to hold the right side of the motherboard (see the pictures). This isn't the easiest thing to do. I included the layout of my acrylic board (see picture). Note that this layout works for this particular motherboard only, and you may need some adjustments to fit other motherboards.
Then everything is easy. Here I intensionally picked parts with a blue tone. Every piece of PCB in this machine is blue. So are the SSDs and the CPU coolers. I am not a fan of case lighting (especially blue light), but the Deepcool Gammaxx 400 was simply cheap during the Black Friday, plus their square outline matches the case well.
One more trick for dual CPU workstation build is that, as far as I know, XFX TS-550 is the lowest wattage PSU that natively provides two 8-pin EPS12V cables for two CPUs. 550W is sufficient for two high-end E5 Xeons plus a mid-range video card.
Finally I want to mention that despite being cheap, the motherboard does not come with an I/O shield. I had to DIY one using thin plastic sheet (see pictures).
Hope you like it, and happy holiday!