Avram in MD: I do agree with you that there is a point when it becomes “too fast”. The description you give does lend to being “too fast”. The minyan where I daven isn’t tied to an end time. We try to finish (starting from Rabbi Yishmael) in 33 minutes (Tuesday, Wednesday, Friday ) and 38 minutes (Monday & Thursday) to accommodate those who have to be in work early. If we don’t then they just leave before Aleinu.
As to your question: “Also, what is the limud zechus for ultra-fast davening on Yom Tov, such as blubluh’s experience?” No time was actually given. We don’t know the paramaters of what bluhbluh calls fast. I once davened for the amud at a Bungalow Colony on the first night of Shavuous. Maariv took 12-15 minutes. Is that fast? What is extra then on a weeknight? Using the proper nussach? Yom Tov Shemona Esrei has less words then the weekday shemona esrei.