Your Kindle will draw no power for the screen in sleep mode. Think of it as a little like an etch-a-sketch. It only uses power to refresh or change the screen image. To not see any "screensaver" I've always had to do that manually. None of my Kindles have ever gone to a blank screen automatically.
I only ever go to a blank screen when I know I'm not going to use the device for a week or more. During normal use I simply close the cover and it goes into Sleep mode. I don't believe going to a blank screen increases battery life in any noticeable way.