SQ competition gets used way too often as an example to follow for daily systems. SQ competitions are judged at low volume levels (I know the norm use to be 126 db, I dont know if that's changed recently). An award winning SQ setup may fall flat on its face in daily use as the 'ground pounder' most daily listeners tend to prefer. Just like for SPL setups, lessons learned from SQ competition installs must be taken with a grain of salt when translating those conclusions and techniques over into a daily system.
If you have the ability to tune it well (EQ, xover, etc), having too much cone area is almost never going to be a problem for a SQ situation. 'Headroom' is a concept that applies to speaker excursion as well, not just amplifier potential.