Read Damon R's wheel stiffness testing observations. Now, make sure before you sell more plasma for that special set of wheels, that the information he shares acually matters when it is applied to the type of riding you do.
"The load is 25.78 pounds (11.7 kilograms or 115 Newtons). There is no magic significance to the 25.78 pound load, but it has some advantages over larger or smaller loads:
It is large enough to avoid some of the difficulty of measuring smaller deflections at lower loads.
It is small enough not to damage any wheels.
I have a convenient 25 pound weight that hangs nicely from a 0.78 pound rod ;-)."
---D. Rinard
http://www.sheldonbrown.com/rinard/wheel/index.htm