Performance issues with StorageTek D173 SAN / Solaris on Sparc

Hi all.

I have a second hand Storagetek D173 disk array, that I am struggling
with performance (or lack of)

It has six 10k, 73GB disks and dual 1Gbit controllers (everything is
fibre) Currently all the disks are configured in RAID0 (it was RAID5,
but thought it might have been that slowing it down)

It is connected to an Emulex 7000E in a new Fujitsu PrimePower server
running Sol9.

The problem is the max speed I have ever managed is 18MB/s (RAID0
across six spindles!) This is doing a sequential copy onto or off the
array. eg 1-2 GB sized files

In comparison copying between the two internal disks (10k, 73GB) I get
25MB/s.

If I watch the Performance Monitor in Santricity I only get 50 IO/s
max, which seems very low

Any ideas what to kick, or do I expect to much?
Thanks for any help
Steve