What comes to mind first is simply measuring the decay time of a plucked string for both pickup configurations. Use protools or equivalent to record and measure the time from point of contact to 50%, 30%, and 10% of max signal. One configuration or the other should show a longer time to decay, implying lower string pull. The hardest part will be getting consistent and equivalent string plucks, but you should be able to average out several samples. You would also need to be careful about keeping pickup height the same between configurations. After that, all that's left is updating your SSC features/benefits list with one more benefit!