I personally feel that, for designing a high class presentation, we require more targeted approach, I have seen people are creating slides just full of the content they don't even care about user point of view. they just put all the content they want to include in their presentation, and in last that become more so unclear and cluttered that they message we are looking to pass through slide won't come out. the solutions for this kind of issue as Tricia said use 7*7 strategy, I think this will be able give better user experience in our slide.