Which unit has the faster cpu and ram between the B810n and 5N2?
The b810n will have higher read/write performance because it has more drive bays to stripe across.
If you see yourself already using 4-6TB drives on all bays on a 5 bay chassis, the b810n will be a better platform for you.
Is there enough network bandwidth for that to matter? The 5N2 seems limited by the gigabit ports and not the drives installed.