How many watts do you really need?

Professional sound level meters will do peaks.  You may not see it on screen because it is not displaying the sound level fast enough, but it will store the peak in memory for subsequent readout.

You can also record "L" values (e.g., "L5") which would be the sound level exceeded X% (e.g., 5%) of the time.  These are typically used in regulatory compliance.  For example, an ordinance may specify that the sound at the property line is not to exceed a level of 70 dB for 15 minutes per hour (L25), or 65 dB for 30 minutes per hour (L50).

The display shown here is in "Fast Response" with "Linear Weighting."

https://youtu.be/P1R2dKRDFUk

I am in the low watts camp.  When I lived in NYC Sound by Singer was my dealer and sometimes High End luminaries would be in the store; on one occasion it was Kevin Hayes of VAC.  At the time I had a Ren 70/70 in my VT home and a 30/30 in NYC.

He opined that (at the time) the 30/30 was his best sounding amp!  However, he could not make any money selling them as few people would pay enough for a 30 watt amplifier.

My speakers are 87 dB at 1 meter for 2.83 volts - 84+ dB at my listening position.  That is 2 watts into 4 ohms.  My 2A3 Elekit amp, good for almost 4 watts, allowed 87 dB - loud enough for most listening.  To forestall comments on the  3dB drop off between 1 and 3 meters the square law drop off is for point sources, radiating spherically, not cone drivers.

For a while I was using a C-J 62 Special Edition - that is a very good amp with many wonderful qualities, and I could blast Mahler but missed something that the 2A3s had.

I am now breaking in a PP 2A3 - good for 14 (gorgeous) watts and 90 dB plus of I want.  This amp is (probably) end game and I'll be posting about the journey to acquire the amp.

@kennyc 

"I think of headroom as an amp that simply loafs along meaning the amp operating at their best sonic level and not strained often leading to increased distortion."

Have you ever noticed that solid state amplifiers reach their lowest distortion just before clipping? In general, the first watt is most important since the bulk of the program from any source is reproduced well below that.

Parasound JCA100 Tribute monoblock power amplifier