The server machine got a makeover.
New Mobo, cpu, and OS.

Now it’s running on an Athlon64 3700+ (socket 939) with 1gig ram.
The RAID 5 was also re-built, all running off 4x250gig SATA drives. After a bit of testing, between the onboard SATA controller and the Promise TX4 SATA300 controller card, I found the best speeds to be when 1/2 the drives are on one controller, and the other 1/2 on another.

#hdparm -t /dev/md0 gives me somewhere around 190MB/s

So far everything is running smoothly.