Ive never blown a speaker while overpowering, it has always been from underpowering. The energy from the clipped siginal is what heats up the coil and to the point where the designed cooling of the woofer cant keep up and you make smoke. Distortion is the number 1 killer of any speaker. Distortion is created by clipping, and clipping occurs when you are trying to get more from the amp then it can give. It is always better to overpower a sub then to underpower it the overhead the the amp will have is what will prevent the siginal from becoming clipped if your gains are set correctly.
Zapco Reference 360.4: H-Audio Soul, x2 right side
Zapco Reference 360.4: H-Audio Soul, x2 left side
Zapco Reference 500.1: JL Audio 10W3V3 Stealth box