Shocked. Need Opinions. How muck power do I need?

Although I’m not sure about the accuracy of the VU meters on my former Vincent hybrid amp, but it  never used over 3 or 4 watts during any of my listening sessions typically up to 80 db measured at 10 feet.  This is driving 87db sensitivity KEF R11 speakers.  I’m now running a Linear Tube Amplifier (Class A/B tube amp) with 51 wpc and never have had any problems. 

this the most interesting thread I have read in a while and such good answers to the OP's question.

I have a theory that has borne out to be true to my ears and understanding as an eleectronics tech and just the different amplifiers I have lived with. Like many people, my original audio setup was very modest, at 5 wpc using a Heathkit stereo receiver, it was replaced with a 40 wpc (Dynaco SCA80-Q) and then a Hafler DH-200 at 180 wpc into 4 ohms, then an Adcom 325 wpc amp, and finally a variety of Carvers at typically 650 wpc (1.5t) was my fave of the bunch - The Carverrs were all 450 wpc or above and always each step taken up the power scale produced to my ears better sound at any level. So my theory is if your speakers are rated at 300w continuous than an amp of double that power is sufficient. This way amp will never struggle to handle the load no matter the source material being played, and it will never go into clipping or even close to it. This protects tweeters and provides the best possibility of clean output from the speakers. Anything less is a compromise.

@ssg308 - I had to laugh when you said its all class A, not because its not a great path to true hi fi, but I am gonna need to say some prayers for you in the summer time with those space heaters amping up the heat in your chilling space...and also for your monstrous electric bill. I can only imagine how much the power company loves you. But ultimately this hobby is about making decisions that are ultimately compromises in some way, some of them financial for sure with both the cost of the equipment and maintenance thereof and the power necessary to enjoy 115 db during some rock concert or movie that you want to hear at reference level or above. So many paths are valid ones to get to audio nirvana. :)

@tomaswv Others have already explained the relationship between wattage vs. db and speak efficiency. I'm only going to add my practical experience.

I used to have a pair of Hafler DH-220 kits that I installed their bridging kits into. When in bridged mode, the amps each provided 440 watts. I figured this would be a cheap way to get current to push my ESL panels easily. The problem was that the ESL are an unstable load. Eventually I switch them back to stereo mode and used only one channel from each to drive my speakers. 

The change in quality was amazing even though I went from 440 watts down to about 115 watts/side. More detail, more bloom and no loss in bottom end. This experience taught me "power" isn't everything. But the quality of the power is supremely important.

Since then I've moved on to an ARC VS-110 and am delighted with sound and still have plenty to rock the house should I choose.

Happy listening. 

@livinon2wheels lets get something straight. 

A. My amp is Pass X250.8 so by definition is not class A amp it is A/AB class amp that runs first 15-20W in class A and it working temp regardless of class operation is 119F. Its not the coolest running amp but its far cry from Pure Class A working temp.

B. It is not a STASI circuit so it does not stay on 24/7 and idling at 900W, there for my electric bills are not so bad up to date $76.92 was the highest bill since I got the amp running and opposite to my Threshold S550e it consumes less power at idle.

C. Yes it s a hobby so by definition you have to sponsor it, now, do you buy records ? CD's? if yes you know your choices are what makes that hobby yours... so are payments and all cost associated, If you are not ready to pay up, don't get in to it, like every hobby that one gets expensive as well.

The sound quality is your reward, take it or live it...