im lost here...
why did you recommend a server board and have him get a normal G3220 cpu?
He would be required to get a E class to use ECC.
Or did I miss somewhere on the intel spec sheet that stated the G series can use ECC?
Also, the atom board he linked is a pretty solid atom server board which natively takes ECC.
It also has a lot more onboard SATA ports...
12 SATA ports on the ASrock vs 6 SATA on your Tyan.
It was designed by ASrock from ground up to be the Ideal NAS server board.
The C2550 Atom is not the typical ATOM processor I think your assuming it to be.
And it will draw a lot less power then the setup you linked by a noticable margin if you factor in the 24/7 on.
http://www.cpu-world.com/Compare/94/Intel_Atom_C2550_vs_Intel_Core_i3_i3-3220.html
ZFS is not clockspeed dependent, its more memory dependent hence the large requirement.
So the OP will not notice any difference on the C2550 vs the G3220.
The only thing I would be wary of however is the fact its made by Asrock, which isn't enterprise noteworthy as per say supermicro / tyan.
To the OP.
I am also looking at that exact board for a new NAS setup.
It is really attractive because it has 12 SATA and can take ECC.
The other route would require you to get dedicated controller cards in order to get the extra sata ports.
But as I stated, the brand name ASrock kinda scares me.
I know they made nice stuff, but they have not been in the enterprise sector for a very long time.
Infact they started making budget class boards, which is typically not the route a enterprise based manufacture would take, as just being labeled enterprise usually carries a 200% price increase over its regular consumer counter part.
I would probably say its ultimately down to how many drives you intend to load your NAS with. If you did not require 6+ drives, then dave's recommendation is solid, however I would select a E class cpu for ECC compatibility.
If your intending to use more then 12 drives, then I would probably go with the ASrock, because getting dave's setup + a dedicated controller + battery backup for the dedicated controller + the fan out cables required for the dedicated controller, will probably end up costing you more in the long run with a lot more complications.