Another strong vote for FreeNAS. I deliver close to 3Gbps via NFS and 4 Gbps via iSCSI throughput off of a FreeNAS setup w/ 8 ssd's in a r10 config for my vSphere storage.
Have you compared other Open-ZFS platforms or genuine Oracle Solaris ZFS?
From most comparisons that I have seen, network performance on BSD, Linux or Solarish can be similar, can differ depending on quality of drivers where general driver support is mostly Linux > BSD > Solarish. ZFS performance is mostly best with genuine Oracle Solaris with a slight advantage of the free Solaris forks over the other Open-ZFS options, propably because the whole internal memory organisation of Open-ZFS is yet based on Solaris memory management (There are efforts to make this platform independent).
In many comparisons NFS on Solarish (where NFS comes from, just like ZFS) is slightly faster than on BSD/ FreeNAS. The multithreaded Solaris SMB server is also often a little faster than SAMBA on any platform (beside SMB3 improvements that are only available currently on the Illumos distribution NexentaStor5, not on others like OmniOS/OI or Oracle Solaris unless you use SAMBA on Solarish).
Whether you prefer the Web-Gui on FreeNAS/Nas4Free/ZFSGuru on BSD or OMV on Linux or napp-it/ NexentaStor on Solarish is a different question. Basically the performance/feature relevant question is BSD vs Linux vs Solarish as it is the OS that really counts not the Web-Gui.