Here's some things that will explain some stuff about batteries. you want them to be warm, not hot when charging them up. They tend to have a little more capacity when warm. The back draw to warming them up is that they also increase internal resistance.
So it should come ideally that when you are racing, you would want to keep them cool, but not too cold, to lower the resistance for increased battery proformance.
When I was in High school, I was in a class called transportation of the future. The class built two race cars from scratch. They were 3 wheeled machines, built out of titanium, and powered by two car batteries hooked up in series. When we charged them for a race, we would stick them in the pick up truck, and keep the truck running with the floor heaters cranked up full blast while charging the batteries. After we slid them into the race cars, just before the race would start, we would tape on as many ice packs we could to help keep the battery cool. We noticed a huge diffrence of not only increased power, but also longer run times. I did feel sorry for the drivers though, as they had to stratle one battery and use the other one for a pillow/head rest.
I wouldn't reccomend going to that extream for RC batteries, since they are more suseptable to temperature variations, but just to show that temperatures can and do make a diffrence.