I understand re. your power bills. I'm running 2 x Q9650s plus a skt 939 AMD Athlon X2, 24/7, and they cost me about A$30 per month I think. That's quite affordable to me, but I do have concerns re. the extra amount of CO2 put out there by the coal-fired power stations used here. The AMD will be going shortly.

Here are a few suggestions of new things for you to obsess about, and perhaps optimise your power use:
- Get a mains power meter to guide you in weeding out the thirstiest of your machines, and to test the effects of any changes you make.
Google "power meter": Choice: Multifunction power meter (I have one of those), ATA Power Usage Meters and Test Gear
- Reduce the power used by the machines that you keep.
. . High-end graphics cards are really thirsty, so unless you you use a machines for games that need them, switch to low-end video cards, even old PCI ones. Or even run without video - see BOINCview.
. . Disable any motherboard features that are not in use such as extra Ethernet ports, Wifi ports, or 1394 ports.
. . Remove unnecessary drives such as floppies, 2nd HDDs or DVDs. Get USB ones which can be plugged in only when needed.
. . Test the option of running more CPU cores slower with less voltage (undervolt/underclock) vs running fewer machines faster.
. . Sell your used equipment NOW, otherwise it will have become more obsolete when you do so (collectibles excepted). That will give you many hours of amusement and frustration. And I think eBay has the monopoly.

If you get a power meter, don't forget to use it to test your monitors. My AOC 210V 22" LCD unit uses 21W in use (low brightness), 9W on standby, 9W powered off using its power button (!!!) and zero when I unplug it. I also have my ADSL modem/router on a timer, so it comes on for 15min every 4 hrs, saving 9W when it's off.

I have another option, that I think is unavailable to you. My electicity costs are:
Peak (2pm -8pm M-F): A$0.33/kWh
Shoulder (7am-2pm M-F, 8pm-10pm M-F, 7am-10pm w/e): A$0.12/kWh
Off-Peak (10pm-7am): A$0.07/kWh
I'll be powering off some machines at obvious times! - HTH