In his book "Star Ware," Philip S. Harrington relates the outcome of an interesting test made by the staff of Sky & Telescope magazine as printed in the March 1992 issue of Sky & Telescope, an issue I missed. It is well worth repeating so I will paraphrase Mr. Harrington here:

The test was made to determine the ability of observers to tell the performance difference between telescopes where the only difference in the telescopes was the wavefront errors in their mirrors.  A master optician produced four 6", F:8 mirrors with wavefront errors of 1, 1/2, 1/4, and 1/10. Two well known veteran Astronomers were asked to rank the telescopes by quality without knowing anything about the telescopes in advance. The veteran observers had no difficulty ranking all four telescopes in their correct order.  More than 300 casual observers were asked to do the same thing.  The majority of these observers could not distinguish between the telescopes with 1/4 and 1/10 wavefront errors, but could tell that both of these were better than the telescope with the 1/2 wavefront error.  Everyone tested agreed the telescope with a wavefront error of 1 was the worst.