Antminer S1s with standard cp2102 usb to TTL serial connections, undervolted, underclocked:
I really like the stack, and 1.2W/GH from that is pretty impressive!
you might find some advantage to run the boards vertically oriented rather than horizontally - it will better force heat upwards and out
the plan is to get all my leftover boards done, and put them vertically into a case, this is just my test bench setup :-p
and we are working to get the watt/GH ratio downward even more :-p