My official line has always been that if you can generate 102dB from one speaker at 1 meter anechoic, then you will satisfy most audiophiles most of the time. That would be 99dB speakers for SEX, 96dB for Stereomour, and 93dB for Paramount 300B amps. This is approximately equivalent to the THX home movie standard and is really quite loud!
A lot of people - maybe half? - are perfectly happy with 6dB less. It depends on taste, preferred music, room acoustics, and speaker directivity.