Personally, I think 'brisk' is a pretty useless term. (I actually had it described to me as between a crawl and flooring it.) If you watch the recent video from Wayne, it will show him advising, keeping it in EV mode below 16 mph, and then admonishing the driver to accelerate to the 3/4 point, IIRC, on the HSI. People who want to think of hypermiling as slow will quote the first part, while those who want hypermiling approval for fast acceleration will use the brisk part. Wayne actually has NUMBERS for both of those behaviors.