I don't "measure" with my ears, but I do trust what they hear.
Not just gain but also one of the reasons people often feel speakers sound "better" with a new amp is that they are able to turn it up louder with less distortion. That's the natural first thing to do...crank it "let's see what this thing can do!" With the correlation being that it sounds better, when in fact it sounds no different and is just louder. That's a perception thing, it isn't wrong because there was an improvement in SPL capability, it is just how it is interpreted by most is that there is a difference in sound IMO.