I just went downstairs and measured the flexibility of three planes.

Here is the data, someone else can compute if there's any of that
to be done...

All three planes were supported 1" in from their extremities and
a 10 lb weightlifting weight was placed vertically and straddling
the plane right over the mouth.  The deflection was read off the 
sole, in the center, about 1/8" in front of the mouth.

                     distance                
    plane         between supports          deflection

  old    #8            21-3/4"                 0.0020
  2 pd   #605-1/2      13"                     0.0005
  CDN SW #5            12"                     0.0008

Paul

Montreal (Quebec)