If you're penny pinching also have a look at your network equipment. As a test I set all switch ports on my 24 port HP from 1Gbps to 100Mbps and the power usage dropped by 10W. About half the ports on the switch are occupied. But then again, with the current prices it might make more sense just to replace the hardware with a newer more efficient model and it will pay itself back in a year instead of 5.