Depends on your music, too. Material with unusually wide dynamic range or crest factor demands a lot of power. Power requirements do not scale linearly with increased subjective loudness, they go up exponentially. Double the power yields +3 db, which is only subtly louder. "Twice as loud" subjectively is approximately +10 db, which requires 10x the power; +20 db requires 100x the power; +30 db requires 1000x the power...that last instance is kind of extreme, but if your average level is, say, 0.5 watts, a not unrealistic average power level, then that 30 db uncompressed snare hit (or whatever it is) will command 500 watts!