TLS Guy is right. Those numbers are mostly just speculative guidelines. It's all about how hot the voice coil will get when you run current through it. You could kill these speakers easy with less than their rated power handling if you put all that energy into the right kind of signal. The KEF speakers would be easy to kill, as would the acoustech speakers, if you fed them the right signal. Think about how hot a filament for a 60 watt bulb gets. Yes, there is a lot more mass in a voice coil, and a lot more cooling, but all you have to do to destroy it is burn off the adhesive that binds the coil- you don't have to get it so hot that it melts the copper windings. Feed any of your speakers a 70 watt signal that is just a 10 kHz sine wave and see how long it lasts.