If your kernel support OC/UC (as Cognition's does), I'd highly recommend useing SetCPU to Underclock to 200/500/conservative for screenoff - I had 2% drain overnight with 3G sync on for GMail/Facebook/Accuweather etc.
Have set the normal profile to 200/800/Performance too see how that rolls.
The other awesome thing about UC'ing when the screen is off? Charging speed are rampant! About 1% a minute, which is way faster than normal!