With 32Kb stripe size and 3 drive raid 5 I see a tremendous improvement in the 10GB network transfer test however it is still a little slower than a single disk. On top of that it is significantly slower in a 1GB windows dd zero write test (15 sec vs 90 sec).
On a linux system with the same hardware and software raid5 using 5 disks I get the following:
# dd if=/dev/zero of=test.test bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 3.42419 s, 306 MB/s
I think I have spent enough time on this one and I will go with single 750GB drives over 3x 500 in raid5 and use the extra drives in my linux software raid servers.