How many watts do you really need?

4 simple statements which oyu must trade off

1. depends on efficiency of speakers

2.  ... and how loud you listen and your room size

3, Volume is correlated to power in watts logarithmically so 10X the power yields 2x the volume. Its. closing game

4. But, all things considered, more is better  for a bunch of reasons

(but things are not equal necessarily since more plower costs money that might otherwise go into, say, better parts)

So everything else is a simple opinion, a data points or misleading.  Figure it out with facts. 

My CODA #16 (that I sold) had the first 100 watts in Class A and total of 150 | 300 | 600 watt @ 8 | 4 | 2 Ohm. Compared to other amps that I owned that were 500+ watts at 8 Ohm and more at lower Ohm. The CODA was much more powerful. That was because the power supply on the lower wattage CODA was a beast.

I now own the slightly warmer CODA #11 which is a lot cheaper and matches a bit better than the #16 to my system. The #11 is also has the first 100 in Class A and is almost as powerful as the #16.

I like class A, but only to the point of becoming a major space heater. 

@kennyc Not me but the Gryphon company seems to believe so, as do a lot of people. “Pure Class A operation has, since we introduced the DM100 in 1991, always been a Gryphon hallmark, because no other circuit topology can match its sonic perfection,”

@gkelly They're quoting actual humans from very respected companies. The fact that you discount anything from that website says more about you than them.

This is an interesting question. Usually you probably wouldn't hear if you were just slightly running out of power. I had an interesting experience with a new McIntosh amp.

A little over a year ago I bought a new McIntosh MC152 amp (rated at 150 wpc), with a speaker protection circuit called Power Guard. Here's a brief explanation.  "a proprietary, patented signal overload technology designed to prevent amplifiers from clipping and over driving, which protects your speakers from potential damage. It continuously monitors both the input and output audio signals, making micro-adjustments in real-time to preserve sound quality".

My room is fairly large, and I have MoFi Sourcepoint 888 speakers with an average of 6 ohm impedance. During a listening session I was listening to AC DC Thunderstruck. It was sounding so good, I kept slightly turning it up. At one point I noticed the Power Guard LED's were slightly flashing. This told me I was starting to run out of clean power. It still sounded great, no distortion to my ears, but this sort of bothered me. I would feel better with a little more headroom. Well, I traded it in for a MC312 (300 wpc with a 2.7dB headroom). Problem solved. I think better to have too much and not worry about it.