http://www.youtube.com/watch?v=MfiSyDErDNQI would argue that this^ is the ultimate in piano perfection for various reasons... but then I would have to wonder what your opinion of the ultimate piano piece would require...
Very nice. I'm not prepared to identify the ultimate in PP; just PP. And there are certainly many examples -- including some Bach -- of PP. (Unless, of course, there can be only one instance of PP, given a particular understanding of perfection?)
Well I suppose it would have to come down to what we are looking for really... personally I would say that in terms of structure, The Well Tempered Clavier is the reason we have the piano in the format that we do today; and thus leads us to the result of any other perfect pianist. However, this does not state what would be the strongest in terms of performance or style of any sort, so that would lead to much more personalized debate.
So perhaps you've put your finger on an orignal, generative instance of PP; and, yes, for me to identify any particular performance/style/genre as an instance of PP is to wade knee-deep in the muddy waters of personal preference (or "taste").