When giving a talk, and I realize 10-15 minutes before the end that I’m not going to cover everything, don’t speed up. There’s this oddball temptation to “cover everything”, but it’s a chimera – if I speed up, chances are very good that most of my audience doesn’t follow, so what have I gained? Nothing.
The better stategy is to pause for moment to gather my thoughts, decide what the most important remaining point is, and then spend 5-10 minutes making that point in the clearest way possible. Hard to remember in the heat of the moment, with the illusion of completeness beckoning.