The DiskTester fill-volume command (part of diglloydTools) was used to test this RAID-0 stripe of four Hitachi 7K3000 3TB hard drives in a 3.33 GHz Mac Pro 6-core. It emits graphable data to show the performance across the volume.
This kind of performance is perfect for speeding up saves of big Photoshop files.
Of course, fast 6G SSDs can be striped as well. However, the Mac Pro motherboard SATA bandwidth maxes-out around 640 MB/sec.