I believe it is the Marvell RAID, are those SATA III ports? Dump them!
Put the X25's in the Intel ports, and set the Drives to RAID in BIOS, and then set up the RAID upon boot up (<Ctrl>+<I>?), there will be a menu for this on BIOS posting.
You will have to reinstall the OS!
BUT, that HDTune benchmark is from the Hard Drive!!!!!! Try running it again, pointing the the RAID Drive!