How Much Difference Does a More Powerful Amp Make?

A couple of years ago Hi-Fi+ published and interesting review, where they compared three Conrad Johnson's power amps- LP70, LP140, LP280, which use essentially the same design, circuit and type of output tubes, the only difference being, as you could probably guess, an output power-70, 140, and 280 Wt. respectively.
Without going into much detail, the bottom line was, that in the same system (actually with some fairly efficient speakers), every more powerful model sounded better, than the one with the lower output. LP 280 was an overall winner.
I completely concur with the above based on my personal experience.
Power of the amplifier has very little to do with the loudness, or efficiency for that matter. It has more to do with the ability of the power amp "to control" the speaker, allowing it to play at it's full potential. Obviously, it has direct impact on how the dynamic aspects of music are being handled.
In essense, you can make 10 Wt. amp to play almost any speaker loud enough, but it won't sound good doing it.

Maril555 - Imagine 100W class AB transistor monoblock that dissipates 100W of continuous power into heatsink while driven with the sinewave test signal.

Now, get rid of this large expensive heatsink and replace it with 25W heatsink and use saved money to oversize power supply and up the voltage. You'll get an amp that is rated only 25W continuous but is louder with better control of the speakers at the expense of continuous power rating that is useless since average music power is only few percent of peak power. Peak power is what counts.

Most likely it will not sell very well since most of people, you including, believes that higher continuous power rating means better sound. Tubes might be different story - we need to ask Atmasphere (he knows tubes).

I have a 100 watt solid state amp that controls my speakers better than a 150 watt solid state and a 400 watt digital amp that I tried.

Approaching your question from the speaker side.
Sensitivity is not the end of the amp/speaker problem. 'goodness' of load is more about phase angle then just sensitivity. A very highly reactive load will be worse, even if much more 'sensitive'.

From the amp side. IF....you were driving just a resistor, the more powerful amp would indeed be slightly louder. Not even 3db, which would hardly be worth it. But, the load you are driving is not a resistor so as it turns out, amps vary in ability to drive such non-resistive loads. It is just possible that the lower power amp will be a better electrical match for your current or proposed speakers.

For the above reasons, 'hi-current' amps may be a red herring non-spec. Since speakers are not a resistor, the real measure of an amp is how well it does into a real load. Which the published specs don't help with.

As for 'real world' performance? Read Kijanki post above. 10x power=2x loudness. Not much for such a huge increase in power. If all speakers were of the sensitivity they advertised, much better leverage could be gotten with more sensitive speakers than the amount of amp power you are talking about.

Check out this link for real-world amplifier testing.

http://www.sonicdesign.se/amptest.htm

IMHO, and perhaps more so with ss amps, having some extra power beyond actual use, is worthwhile in that it can keep an amp from stressing near it's clipping point.