I've had pretty good luck buying rack servers and workstations for HPC from Thinkmate (http://www.thinkmate.com http://www.thinkmate.com). Their systems come pr

I've had pretty good luck buying rack servers and workstations for HPC from Thinkmate (http://www.thinkmate.com http://www.thinkmate.com). Their systems come prebuilt but their markup is pretty reasonable, considering they give you a known-good configuration. You can pick and choose whatever combo of Xeon's + GPUs you want [read: can afford].