I was trying to match the marketed spec as closely as possible. At this stage there seems to only be one board (that I could find) that supports the E5-1620v2 with ECC. It lacks USB3, has only three PCIe slots and generally isn't up to spec.
Building another high-end PC (i7-based) to out perform the Mac Pro is a whole different excercise, and I'm fairly sure it would be quite a bit cheaper.
Right, but I mean he should have dropped the CPU if he wasn't going to use ECC; the big advantages of the E5 are SMP and ECC, neither of which he was using. An i7 will be clocked higher and cost less, and come on a more useful motherboard for most workstations.
Building another high-end PC (i7-based) to out perform the Mac Pro is a whole different excercise, and I'm fairly sure it would be quite a bit cheaper.