What you gave was a rule of thumb type answer, which is basically just a wild ass guess, I would hardly call it accurate. I don't know where you came up with this other formula but music being 1/3 the current draw of a tone is another wild ass guess which is highly subjective to the listeners music tastes. That may be accurate for someone that listens to regular rock or other normally recorded music but someone who listens to rap or any of the slowed/modified songs that get posted on the forums will have a much different experience. A lot of those songs basically DO have test tones in them. The bass notes are just solid sinusoidal notes, some held for much longer than average which will definitely violate your 1/3 rule.
I think you'd be surprised.
For one, I'm not sure you fully understand what a 0db tone is.
There's also impedance. Any given sub is rarely at nominal impedance.
Most bass heavy songs I hear have a kick at the front of the wave and fade into something relatively soft. If you measure that second (or so) of energy in the wave against a 0db tone of a similar frequency I would expect it to have significantly less.
The 1/3 "rule" isn't a rule at all. It's something Richard Clark mentioned years ago at carsound in a discussion about current demand and how much amplifier power could be run with a certain size alternator.
He said something to the effect of music with a crest factor higher than 1/3 could hardly be recognized as music. That may have been a bit of an exaggeration, but the point was made.
A few years back I had the chance to watch an auto electric shop's charging system analyzer run while I played Bass Mechanik at full volume. I was running two zed amps totaling right around 1200w rms.
The highest current draw measured was around 65A. It basically hovered from 40-60.
If you've seen JL's school of sound on Youtube - the highest crest factor of the samples they had was actually hard rock - of course that was due to the mid-range material, so in that case a monster sub amp wouldn't be much of a factor.