Power compression becomes "a thing" when you routinely run your system to the edge and keep it there. Where the edge is depends on multiple factors and they're in discussion here
The tipping point is where applying 3dB more electricity does not produce 3dB more acoustic output. Once you're there, going back (thermally) without being noticed is nearly impossible.
Genre DOES play a role in how I set subwoofer limiters - things with lots of kick drum and occasional 808 drop are treated differently than EDM. For the former I'm interested in keeping peak mechanical excursion down as well as long term power limiting; in the latter I'm mostly interested in long term power. Where that ends is a thermal AND xMax consideration (as Mac pointed out) but my experience has been that for EDM subwoofage the long term power limiter threshold turned out to be about 25-30% of "rated" power or power compression would become noticeable after a half hour or so.
I recall an EDM even (I think Fowler may have been involved) where there were duplicate banks of subs and a switching scheme that allowed the provider to alternate between them so the woofers could thermally recover.
