hadn't realised it was an array - what are you HDTune settings? You need to have the block size larger than (number of drives) x (stripe size) or you won't test the max sequential speeds.
I'm testing a single drive, but it is the same for a 2*300gb 15k.7 raid1 array.
Strip size is 128kb and block size is larger....
Firmware is lsi latest for 8408e.