For preference, one could listen to the whole two books of Bach's keyboard mastertext but it would be impolite to ask, too much to expect and any wise performer knows to deliver slightly less than the audience would like to leave them wanting more.
If Bach's subdued eloquence was the last word in organisation and good sense, Schubert's last word in the Piano Sonata, no.21 in B flat, D. 960, is more fitful and uncertain in its early stages. We are less than thirty years after the death of Mozart and that music can still be heard in passages, most obviously in the final Allegro ma non troppo, which didn't seem all that ma non troppo today. But Schubert takes the darker side and some more lush harmonies further and looks forward to Brahms, too. The sonata has apparently resolved much of its crisis by the end and the audience, noticeably rapt in their attention throughout were good enough not to applaud between movements and several took it upon themselves to offer their ovation standing.
This was an occasion, with Kovacevich in tremendous form who shares my birthday but is 19 years my senior, making him 78. Although only eight rows back, I was unable to see him on his stool which makes for greater concentration on the listening but less advantage in remembering what he looked like. Thus, a few minutes after the performance I asked someone to sign my programme who politely explained that he wasn't Stephen Kovacevich. And that, dear reader, is all you need to know about the provenance and expertise of any review of mine you read. Now I'm not sure how many programmes I have were actually signed by the janitor.
How we laughed.