Poor Write Performance

I recently installed DSS V6 Lite and although the improvements with the web interface are very much appreciated, the actual performance of the NAS seems to be degraded when copying large files to the NAS. The previous version we used, from Jan 1st of 2008, didn't exhibit the same quirks. I have tried this in both the 64bit and 32bit versions.

System:
AMD Opteron 1216 2.4GHz Dual-Core Processor
2 x 512MB DDR2 667 ECC Unbuffered Memory
4 x 320GB 7200RPM Western Digital Caviar RE HDD
Areca 1110 PCI-X 64bit SATA II Controller
RAID 5
Intel i82541PI Gigabit Network Adapter

Workstation used in testing:
Intel Core 2 Duo 6600 2.4GHz
2 x 1GB DDR2 1066 Memory
Gigabit Network Adapter
74GB Western Digital Raptor

Network:
HP Procurve 2510G-48 (all machines connect through this switch)

Test file:
5,934,096 KB

When copying large files (>4GB) from the NAS to another machine, there is no problem, but when copying large files (>4GB) from another machine to the NAS, it will pause for a minute or two then tell you that the specified network path is no longer available. You click OK thinking that you will have to try again, but will notice that even though the copy window has closed, the file is still copying. It will copy completely, but it takes forever. I have also noticed that every drive in the RAID array is active straight time while the large file is copying. I would only expect periodic flickers since that is what it does when copying from the NAS to the workstation.

When copying from the NAS to another machine, the network traffic runs around 25% +- 5% or 31.25MB/s, but when going from another machine to the NAS, the speed is much slower. I would have a more concrete number, but suspiciously when the files are copying (since they still copy even though the copy operation according to windows fails) from the workstation to the NAS, neither my workstation, the network switch, nor the NAS report any traffic.

I don't have write cache enabled on the RAID card simply because I wanted to avoid losing data in the case of power loss during a write operation.

Any help would be appreciated. Unless there is some kind of solution, I think I will switch back to the older version.

Thank you,
Justin