In the olden days of Pentium 3 (or Pentium!!! if you prefer), one guy graphed his Peltier element's performance vs. voltage and found a 115% efficient point (with assistance of his fan, ofc.)

Limiting voltage and coupling it with a very efficient cooler for its time, he overclocked his CPU a great deal.

Looked for the article, but it's possibly gone down with the downfall of old internet, because it was a personal webpage.