Lore has it that Bob Pearson made a good guess at the best-glide-speed of a 767-200--the Gimli Glider--and came up with 220 knots IAS. I don't know if he looked it up or not, but the legend is that it was "because he was a glider pilot."
Why, forgodsakes, do they always call sailplane pilots "glider pilots"? Gliders go down. Sailplanes go up.