From the conclusion:
The conclusion for our reissued battle between the current 150 GB WD Raptor and the pair of 400 GB WD4000KD hard drives in RAID 0 is surprising. Although the WD Raptor clearly remains the fastest Serial ATA desktop hard drive, the RAID 0 array beats it in most benchmarks except access time and I/O performance. The cost per gigabyte ratio of the Raptor is particularly questionable, as you can get three times the storage capacity for half the money today, which has mainstream drives beating the Raptor by a factor of six. Enthusiasts willing to accept the higher risk of data loss in RAID 0 should carefully consider a RAID array consisting of two cheap 7,200 RPM drives over the WD Raptor.