This is a place to start. Some bikes, however, are harsher/more stiff than others. I have been on some frames that are really harsh, not that there is anything wrong with that per se, but riding my regular 65miler road rides would be torturous on some frames. And when shopping for bike frames, it is important to me that the frame is not super harsh, although I prefer stiff bikes.

Stiff without being harsh is kinda nice.