Undervolting lets you run at normal speeds. You're basically just reducing the safety margin between the default "reliable but excessive voltage", and "at the verge of crashing." Like overclocking, you change the value progressively until you have a crash, then go backwards until you're stable.
BTW a few years I picked up a 1RU server for about $USD 35... at the time I thought I'd grabbed a total bargain, but because of the noisy fans, proprietary heatsinks etc it turned out to be a real headache running it in the office. Better to part it out and sell off the bits on ebay.
