It's hard to say b/c I didn't take any measurements, but the power output was down by about 25%. My little 3D plane would usually hover at 1/2 throttle, but on the cold days it took between 3/4 and full throttle to keep it in a hover.
If you go to
www.ezonemag.com there is a lot of info on Lipo's. They've been flying them in rc planes for close to 10 years now and have a lot of experience with the technology.