Not convinced. I have a Raid 5 array of 4xWD 640GB 7200RPM drives (WD6400AAKS with 2x320gb platters, the most efficient 7200rpm drives.) For a grand total of $400. The boot/swapdisk partitions are striped across the inside of the platter, with larger storage areas towards the outside.
The way i see it, each of those have a 3Gbps throughput, which gives me a theoretical max of 12Gbps. Not that I'd ever see it IRL.
This was before SSD's got cheap. Waiting for PCI-E RAM adaptors to become available at normal prices so I can move the swapfiles onto 8GB of RAM.