Sharing mounted FreeNAS volume
Before giving up on a standalone FreeNAS machine, try the included speed testing tool iperf to determine the best protocol for your network:


  Iperf is a utility for measuring maximum TCP and UDP bandwidth performance. It can be used to chart network throughput over time. For example, you can use it to test the speed of different types of shares to determine which type best performs on your network.
  
  FreeNAS® includes the Iperf server. To perform network testing, you will need to install an Iperf client on a desktop system that has network access to the FreeNAS® system.


Do you know which alternative protocol your clients could use to connect to your FreeNAS box? Are you restricted to only File Transfer Protocol (FTP)?

This recent discussion talks about the some factors affecting FreeNAS, FreeNAS Poor Network Performance.