According to CNN http://www.cnn.com/2007/WEATHER/05/07/severe.weather/index.html.
Moving at 20 MPH, a 1.7 mile wide twister would have 205 MPH or so winds over one spot for, well it's too early for math, but long enough to obliterate a town.
Makes me wonder though... Does anyone know what the widest recorded tornado was? I know one of the ones in Pennsylvania on May 31, 1985 was over 2 miles wide (over state forest land, fortunately). I imagine the Plains States have produced a bigger tornado at some point.
My thoughts go out to the victims of these storms.