As an example. For the last nine months I have had both a set of Audio Research Reference 160m monoblocks ($36K) and a Audio Research Reference 160s (the stereo version, $22K). There is no question the monoblocks out perform the stereo unit and are worthy of the price.
I have found performance levels are largely in line with cost without discontinuity. Different companies have different house sounds of course. The high end audio amp market is highly competitive… any real anatomy in price / performance would get eliminated pretty quickly.