The Tech Report has compared the performance of Serial ATA and RAID.
STORAGE SUBSYSTEMS DON'T GET nearly enough attention, though they're arguably the most important subsystem of a modern PC. Of course, they store all of a system's data—an increasingly precious resource that most of us don't back up nearly often enough. Storage subsystems are often the slowest components in a modern PC, as well. Hard drives are essentially mechanical devices, and even with ever-growing platter densities, their seek times can amount to a practical eternity in computer time. Modern storage subsystems have a trick up their sleeves, though. RAID arrays have the potential to improve storage performance dramatically by spreading data over multiple drives. They can also improve redundancy, allowing a system to survive one or more drive failures with no data loss.