New Orleans definitely did NOT experience sustained, Cat-3 surface winds in Katrina. The city was on the weaker side of the storm, and nearly all of the Metro area was just outside (W) of the eyewall.

The surface wind analysis produced by the Hurricane Reserach Division shows Cat-1 winds hitting the city along the lakefront only: http://www.aoml.noaa.gov/hrd/Storm_pages/katrina2005/katrina_landfall_kt.pdf

The NHC is slightly less conservative. In their Katrina report, they indicate winds of Cat 1 or maybe Cat 2 strength hit the city: http://www.nhc.noaa.gov/pdf/TCR-AL122005_Katrina.pdf

Either way, the evidence strongly suggests that the city did not experience sustained Cat-3 winds at the surface-- as disappointing as that must be to people who lived through that experience.

This having been said, winds were much stronger above the surface-- as is very common-- thus explaining some of the heavy wind damage to the upper storeys of some high-rises in the city.