Got the same, Asus AM1M-A, Athlon 5350, SSD
Best/Least I've managed is about 24,5W draw from wall socket (also using dual slot Intel Pro1000MT NIC).
ECC, haven't managed getting it to work. Tried two different brands, had Hynix and Kingston's unbuffered ECC sticks lying around.
FreeBSD, enabling CPU throttling leads to system crash (unless I disable C6 state in BIOS)
No such issues under Linux but haven't seen lesser energy expenditure there either.
Disabling one/two/three "cores" does not make any difference at all in power draw. Only undervolting works to an extent.
I could probably shave couple of Watts off by making the cooling passive (remove fan) but I am not sure it's worth the trouble. None of the big custom heatsinks seems compatible to fittings used with AM1 socket.