I was re-reading Consumer Report's review of the Gen 4 Prius. Here's what they say about staying on electric power: As before, the Prius can propel itself on electric power alone at low speeds and with a light foot, typically up to 40 mph if you're patient. That's handy in stop-and-go traffic or when you're just loafing along on Main Street. I've read elsewhere that you can stay on electric up to about 25-27 mph. I was looking for the answer in the manual and could not find it. Is there a definitive answer?