Bad RAID1 read performance

Hi,
    after doing the "dd" tests for a server we have at work I obtained:
Read: 47.20 Mb/s
Write: 39.82 Mb/s
    Some days ago read performance was around 20Mb/s due to no readahead in md0
so I modified it using hdparm. However, it seems to me that being it a RAID1
read speed could be much better. These are SATA disks with 3Gb of RAM so I
did 'time bash -c "dd if=/dev/zero of=bigfile bs=8k count=786432 && sync"'.
File system is ext3 (if read many times in the list that XFS is faster), but
I don't want to change the file system right now. Modifing the readahead from
the current 1024k to 2048k doesn't make any difference. Are there any other
tweaks I can make?