The fastest wind speed ever recorded was 318 miles per hour.

This record-setting gust occurred in a tornado that hit the suburbs of Oklahoma City on May 3, 1999. The funnel cloud struck near the town of Moore, OK at about 7:00 pm, killing about four residents and destroying a total of 250 homes!

The speed of 318 mph was only 1 mph short of classifying the tornado as an F-6 on the Fujita scale! No tornado has ever received this distinction.
(source)