Each company is a little different IMO. My 11' 6 wt Imperial Switch felt softer than my 10' 7 wt Helios 2 SH. It could have been that the action was slower, therefore leading me to believe the rod was soft. It's hard to compare rods of different lengths, because the longer the rod, the more rod you have to flex. If the Imperial had been 1' shorter, it may have felt much stiffer, who knows?
In any case, the general idea is that a Switch or Spey is approx 2 line classes up from a SH. Any particular reason you're asking? Maybe someone else would be able to chime in if you had a rod-related question.