Have you tried the ATTO benchmark? I think PCMark doesn't bench RAID correctly at all. My Raptors can hit over 100MB a sec in ATTO, but PCMark gave me an 820!, yeah right. My single 80G 8MB cache could hit 1100, so I know the benchmark is whack.
Another thing is your stripe/cluster size, which you almost always want to match. The default stripe is 16K for many controllers and since I'm not working with large files, such as video editing, I left mine there, 64K is pretty damn large for just OS and games and such. Another thing that may affect performance is your cluster size Windows uses. The default is 4K, if you set that to the same as your stripe size, performance will most definately increase. I don't know how to choose cluster size while installing Windows or if it's even available to choose, I used Partition Magic to change it from 4K to 16K myself. My benches went from 70MB peak to 100MB by changing the clusters to 16K and then defragging the drives.