Trebleclef, you say in another thread that you have P3's in a den driven by a little NAD amp. In this thread you say you have heard them in a used record store. Which is it?
Here's what a friend of mine who has heard both said over at AudioAsylum about the P3ES - S3/5 comparison:
"The Harbeth HLP3-ES may be hard to drive @ 83db/6 ohms (something like that I think), but if controlled properly, can produce one of the most natural midrange and would offer the wonderful level of transparency to your music.
The Spendor 3/5 is a friendlier speaker, in terms of load and also the sound. They will never fail to please. Sonically, the harbeth and spendors might sound very close, but over time, you'll notice that the spendors gives you an "extra" dollop of sweetness, while the harbeths continue to excel in the transparency and imaging."
The Harbeth needs and accepts more power. The Harbeth is probably the more accurate, closer to your Quad ideal and is probably more dynamic. The component parts of the Harbeth are more costly than the parts used in the Spendor. The Harbeth uses a metal dome tweeter, the Spendor a soft dome tweeter. Some people here will tell you soft is good and metal bad, but it really depends on the quality of the particular tweeters being compared.
When you email someone through Audiogon, it's a good idea to tell them your name and maybe where you live unless your email address identifies you.