It's easier to give a long speech. In Toastmasters contests, the time limit is 7 minutes and 30 seconds. I used to own a couple DVDs of the World Champion of Public Speaking competition. At that highest level, the content, delivery, timing, story, presentation are all super polished and honed to a sharp edge. Yes, they all tend to be a tad too motivational but that's what the best speeches tend to be (and the best speakers aspire to be...).

Here are a couple examples (from the same guy - most of the winning public speakers seem to now professionally coach speakers for a living and don't share their speech videos online):

http://darrenlacroix.com/2010/06/darren-lacroixs-winning-toa...

http://www.youtube.com/watch?v=qovsP1aaEQY