Speaker power ratings are always a bit iffy. The best explanations I've seen are "I played guitar and bass through it, and noted the power level when it blew. Then I reduced that a bit for the rating" and "The power rating is the size of amp the speaker can handle without blowing."
Power ratings can be the amount of power the voice coil can dissipate continuously without melting, or for a short time, the amount it can take before the former or adhesive give out (I've read that voice coil adhesive is the most common mode of failure), the amount it can take before the voice coil leaves the voice coil gap, or when it hits the back plate, or when it reaches a certain level of distortion.
Given all those variables, peak v RMS doesn't matter all that much.