There is something shady going on with 4k RAID0 performance. For example on my system with freshly secure erased drives and fresh windows 7 install, I am getting just 26MB random read out of 2x256GB 840PRO ???? While sequential read is 1GB+, 4k read performance is disastrous. I really hope Anand will investigate and put Intel's corporate rear end on fire for such a product in 2013.
Edit: setting cpu in windows power settings to minimal 100% (cpu pegged @ 3.5Ghz all test) improved 4k random read performance - now getting 37MB/s, but still real low...