Strictly speaking, not true. If the lectures were all standardized at, say, 50 minutes each, then a professor that could be sped up more would take less time to

Strictly speaking, not true. If the lectures were all standardized at, say, 50 minutes each, then a professor that could be sped up more would take less time to get through each lecture than one who could not be sped up much at all. It's kind of like how you can read a page with lots of blank space much faster. Of course, it all gets muddled in the question of how much info per lecture\minute is actually best for learning, but if your goal is to get through them quickly then a speedable professor is best.