How strong is a tornado in tornado alley?

The strongest winds ever recorded in a tornado (302 mph +/- 20) occurred in the Moore, Oklahoma F5 tornado of May 3, 1999.
However, actual wind measurements from tornadoes are rare, so other tornadoes may have been stronger, but never had their winds measured.
Another good candidate for the strongest tornado in Tornado Alley is the Jarrell, Texas tornado of May 27, 1997, which produced the most extreme tornado damage ever documented.