Sell it and buy one optimized for power (and perhaps noise - they often go together anyway, as a large part of rack servers power use is the cooling fans that sound like tiny jet engines.) Even if all you want to do is pull processors you can probably do better selling it as a machine fully-loaded and buy one the same but half-loaded than by pulling yours - but that won't compete well power-wise with a server designed from the ground up to save power. A nice efficient tower server can be a lot more pleasant to be anywhere near and might save you 350-400 watts, or more when idle, for 3000+ kWh/year (not counting less air conditioning load.)
That alone will pay off a new-to-you server pretty quickly in lower power costs. If you sell this one, it pays off even faster.
Pulling two processors will lower your power use - somewhat. CD probably won't make a difference, if it's idle.