71 dB
Headphoneus Supremus
0.5 dB is usually a good "rule of thumb" threshold of audibility. In music mixing changing the level of an instrument by 0.5 dB is often somewhat easy to hear, because how much the sound gets masked (below the threshold of hearing at each frequency) by other instruments creates clear audible differences. People with trained ears can hear differences smaller than 0.5 dB (the limit seems to be around 0.2 dB as you mention), but the differences perceived are so small it starts to be a "who cares?" situation.
My home theatre amp can adjust the volume at 1 dB steps. I can easily hear the difference 1 dB step makes, off course, but I don't need a finer scale of volume adjustment. If I want the sound to be a little bit quieter or louder, 1 dB step down or up seems to do the job for me. In other words, getting the volume right with accuracy of 1 dB makes it feel correct even if I could hear smaller differences such as 0.5 dB. I have never felt the sound is half a decibel too loud or quiet. Why? Because typical sound (of music/movies/etc.) isn't a steady signal to begin with. Its level varies all the time anyway. The perceived level is a subjective average anyway.
When I mix my music, suddenly the way each instrument mask each other becomes important and 1 dB adjustments can feel too coarse (sometimes it is enough if the masking happens in a certain way, but not always). If an instrument track is set at level -11.5 dB and the "optimal" level would be -11.6 dB, I am only 0.1 dB off which is insignificant and most probably not audible. If however the "optimal" level would be -11.75 dB, I am 0.25 dB off no matter if I choose -11.5 dB or -12 dB. In this kind of situation it might be needed to do a 0.25 dB adjustment, but these situations are very rare and can be handled in other ways too. For example filtering with a high-shelf filter above 5 kHz just one decibel might do the job even better, but it depends on the situation.
Just because we can hear differences if we try hard doesn't mean those differences matter. All differences that matter are audible, but not all audible differences matter.
Btw, here on sound science forum I'd like to see people write dB and Hz correctly.
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