150mb per drive sounds more realistic, but you will never get 400 read and write without a high quality raid card.It's two WD black drives, they were brand new. Right now they run at 310 according to DXtory, because I haven't defragged or decluttered them since I've used them, and they're full of 5mb video scraps.
got several WD Enterprise HDDs at work and also some raptors and i never got such results (imagine the response time and the cache in comparison to a ssd)