Keep in mind that a VERY important factor in how much power you need is the dynamic range of the music you listen to (meaning the DIFFERENCE in volume between the loudest notes and the softest notes).
One of the most demanding kinds of music in that respect is classical symphony orchestra, if it is well recorded with minimal compression. If you set the volume control to produce modest volume levels at your listening position of say 70db on soft-to-medium passages, brief dynamic peaks on orchestral crescendos, bass drum beats, etc., can easily exceed 100db. 100db requires 1000 times as much power from the amplifier as 70db.
On the other hand, if you listen to typical highly compressed rock music, which may have a dynamic range of only a few db, and you listen at modest volume levels, you will need far less power. For instance, an 85db peak only requires 1/32th as much power as a 100db peak.
Regards,
-- Al