I was actually doing some benchmarking yesterday. I used NFS (which may perform better or our dual core board then the single threaded CIFS)
I ran iperf to our realtek NIC and was getting weird spikes, from my ubuntu desktop to my FreeNAS server through an unmanaged gigabit switch. iperf gave 560Mb/s but I noticed it was spiking to 800+ then dropping several times.
I then did it with an Intel PCIe NIC (you can pick one up cheap) and was getting 900+Mb/s on iperf just fine.
I then wrote a 14GB file of zeros on my ubuntu desktop, got 230MB/s on my new Maxtor SSD, read it at 300MB/s. So my desktop shouldn't be the limiting factor (except possibly for it's realtek NIC).
I then moved the file to the Nas using NFS on the realtek IP, got 50-60MB/s but it drops down slowly.
Read it back to my desktop at similar speeds.
Then rewrote it but this time on the intel IP, got 80MB/s at first but it crept down to 50-60MB/s.
I then read the file and was getting full 123MB/s speeds at first, but it then quickly dropped down to 80MB/s.
I also ran top on FreeNAS and it showed low idle percent, like 9% to 2% so I'm guessing the NFS transfer was CPU bound.
TAKEAWAY (might be wrong)
NFS transfers CPU bound on our motherboard, if your ok with 50MB/s then this board is a perfect low power solution. I have 16GB of ram and I believe the ARC cache came into play when I read the file the second time. The e350 also had to work less because it was sending the data over an intel NIC, not the realtek nic. In actual performance the NIC made some difference but is not crucial.
With CIFS, which I believe is single threaded, you may get even worse performance on this low CPU power board. But I don't think CIFS relies as much on the ZIL so you may actually get better performance.
I believe I could increase NFS write speed by adding a dedicated ZIL drive. Thinking of the Intel 313 but can't get myself to spend the money.
I am thinking of swapping the motherboard for a Gigabyte and g530 but don't need the performance increase so I can't get myself to spend the money either. I could also add 2*8GB of ram and possibly get more caching in. The only problem s I believe the g530 would use an additional 10W when idling which is almost $1/month of cost for me.
Not really worth is for the little performance I get, and the only time I 'need' Gigabit speed is when I move a movie over to my desktop for running mkvmerge, and send it back. But I probably will eventually upgrade just cause...