Looking at reviews of Iomega Storcenter on the web it's not renowned for its performance.

However, what is the network connection between the machines? Can it run any faster? Like increase from 100Mb/s to 1000Mb/s?

Are there any network devices between the systems (eg, hubs, switches) that are slowing the connection down?

Can you increase the cache size on the NAS configuration?

IN PARTICULAR, can you change the cache setting from write-through to write-back? If so, that might make a big difference.

Oh, and what network adapter(s) are you using? Is there something in that BIOS that will improve performance? How many network interfaces does the NAS have? Could you consider teaming interfaces at each end?