For those with further interest in this thread,
Steve Cannistra has done some excellent work in this area. You can also download an excel spreadsheet from his site that helps you play around with some real world values
His take?
CCD cooling beyond -15 to -20 C produces minimal gains in the functional dynamic range for most imaging sites, because the sky flux becomes the limiting factor in this situation.
Roughly translated.....a dark site is way more valuable than a super cold chip! (Why do I have a backyard observatory again?? Doh! )