have you tried nas4free?, im running it via vmware fusion to get familiar with the GUI, the only major difference was that freenas was running a older freebsd version, i havent done any hdd performance to stabilty checks.
nas4free has less ram requirements but you will need the same hardware to get the same performance
freenas has better user interface and design
i was curious as i jumped onto freenas without any prior knowledge outside win/mac but freenas has been great so i dont want to stuff up my files playing around.
the only issue i see is that users had problems with their hardware on 8.3 so they switched
see this image (freenas 8.3)