Coming from someone that uses a BOXX workstation, assuming you spec one to match the Mac Pro, they are the same price.
This one is a single socket machine, and its overclocked.
To those wondering about the hard drives, there are 6 trays in a arrayed fashion behind the mainboard. Thats where they sit. Out of the way, and no overheating. At least on mine they dont, and I have 3 drives.