I heard someone say that "Tempus Fugit" by Yes could be considered as the perfect prog rock track. I don't know if such a canon exists, but I like very much this song, taken from "Drama", one of my favourite albums ever. This is a somehow devilish piece of music, with each instrument engaged in a musical battle against the other ones, and still the final effect is that of admirable harmony and coherence. Just another progressive miracle, I daresay.
The Yes+Buggles line-up in 1980.
Sure, Geoff Downes' sensible touch contributes to the artistic amalgam, but the track is nonetheless sparkling and even pyrotechnical with a stunning series of accelerations and abrupt changes. That's why if I cannot agree with the above draconian quotation, I surely reckon this is great, great prog!