Interesting looking at db measurements with a 4w amp. Speaker efficiency is measured at 1w 1 meter. A 93db rating is a low efficiency speaker, and a 103db rating is high efficiency. That is a 1 watt signal sent into the tested speaker, producing 93db or 103db at a distance of 1 meter from the speaker. Puts some perspective on your 65db cleans for Here Comes my Girl etc. Amps are supposed to be rated at clipping, or at the highest clean output, where it just starts to distort. So an AC4 should put out 4w of clean power, or maybe 3w to be sure it's really clean. 65db kind of suggests the AC4 can't even put out 1w of clean power. A lot will vary in the testing method, but one thing I really wonder is what people mean when they say "loud"? Also of course rated clean output can vary. I have not compared the two amps side by side but I've been told an AC30 is of comparable volume to a 50w Marshall. Likely the AC30 would have efficient Blues and the Marshall would have less efficient speakers. WRT some claims that an AC30 is awfully bright and hard to dial in lower volume tones, while others claim an AC30 is easy to dial in lower volume tones, the speakers play a huge role including the age of the same model speakers. A fresh alnico Blue is harsh and strident, while a well used Blue is fat and sweet. New amps in shops are likely to come with new speakers that are still harsh and strident, until they've been played fairly loud for 30-40 hours. I suspect amps are often judged based on the speakers.