Advertised Vertex 2 speeds are with ATTO & AS-SSD benchmark software.
You need to benchmark with AS-SSD.
Advertised AS-SSD speeds are "up to" 225 MB/s Read and 80 MB/s Write.
So with 2 drives in RAID-0 you're looking at max speeds of 450 MB/s Read and 160 MB/s Write.
Your CrystalDiskMark results of 470.4 Read and 158.8 Write seem to indicate that your RAID performance is ok.
Here's the link to the spec sheet for your drive: http://www.ocztechnology.com/images/OCZ_Vertex2_2.5_AS-SSD.pdf