I found some nice information about tuning FeeeNAS 7.x from a few sources last week.
A blog post HERE made by Learned By Error details some settings to use for tuning FreeNAS for increased network performance. That post combined with information from the FreeBSD Wiki article called ZFS Tuning Guide and a U.S. Department of Energy article called TCP Tuning Guide – FreeBSD Tuning helped me determine the optimal tuning settings for my system. Prior to the TCP settings I was only getting around 25-30 MBps between my PC and the server. Now, with the new settings, I am getting up to 80-90 MBps (bursts) with common speeds of 55-60 MBps.
Here are the settings I currently have under System -> Advanced -> sysctl.conf
