Very low disk performance Highpoint 1820a

I've just finished putting together a new server box spec:
Dual AMD 244, 2GB ram, 5 * Seagate SATA 400GB on a
Highpoint 1820a RAID 5 array.
The machine is currently running 5.4-STABLE ( from the
weekend ) After install I did some basic tests and the
disk is return very poor performance low in fact than a
single disk on a bog standard ATA 100 controller:

5.4-STABLE Highpoint 1820a RAID 5 ( 5 disk )
dd if=/dev/da0 of=/dev/null bs=64k count=10000
10000+0 records in
10000+0 records out
655360000 bytes transferred in 13.348032 secs (49097875 bytes/sec)

5.3-RELEASE Highpoint 454 RAID 5 ( 4 disk )
dd if=/dev/da0 of=/dev/null bs=64k count=10000
10000+0 records in
10000+0 records out
655360000 bytes transferred in 20.410034 secs (32109697 bytes/sec)

5.2.1-RELEASE Intel ICH3 UDMA100 ( 1 disk )
dd if=/dev/ad0 of=/dev/null bs=64k count=10000
10000+0 records in
10000+0 records out
655360000 bytes transferred in 11.142405 secs (58816745 bytes/sec)

Obviously something is seriously a miss here somewhere as
both the RAID 5 arrays a producing less throughput than
a single disk.

Where do I start looking?

    Steve


================================================
This e.mail is private and confidential between Multiplay (UK) Ltd. and the person or entity to whom it is addressed. In the event of misdirection, the recipient is prohibited from using, copying, printing or otherwise disseminating it or any information contained in it. 

In the event of misdirection, illegible or incomplete transmission please telephone (023) 8024 3137
or return the E.mail to postmaster_at_multiplay.co.uk.