Your definetly bottlenecked at the RAID controller PCI 32bit is going to be a killer for the bandwidth on those Hitachi's
Look at a PCI-e x 4 controller to get the bandwidth. Something like this will give you more bandwidth. Im assuming those drives are SAS.http://www.adaptec.com/en-US/products/sas_cards/value/SAS-3405/
The only other things that will slow you down is network connection to other machines and you internet connection.