I wish I could give you a definitive answer. I've been running my NAS as a service on my SunFire V20z, along with web, mail, etc. services. This is a way overkill box for this use. Darn thing doesn't even break a sweat under the heaviest load I can put on it through my network.
Believe it or not, I did put OpenSolaris on a VIA chipset based mini-motherboard several years back in order for someone to run Asterisk on it, so I have proof that OpenSolaris will run well on an low-horsepower, fanless system. As for a NAS, it would seem to me that the only requirements would be ample memory for ZFS and enough horsepower to keep the network maxed out. Which one to choose is outside my knowledge at this time. -- This message posted from opensolaris.org