Experiments with pinhole diameter

The standard formula for optimum pinhole diameter is quoted everywhere, but
has anyone actually done some experiments to see if photographic results
confirm it? I saw a quote by Larry Bullis somewhere to the effect that he
had not observed any diminishing returns in going smaller. Here it is:

    http://www.pinholevisions.org/resources/articles/makingholes.php

Looking at the derivation of the standard formula it seems to make some
assumptions that might not reflect the way we actually perceive photographic
sharpness. In particular the notion that the outer diffraction rings are
strong enough to be perceived as lack of sharpness at all pinhole diameters
beyond the 'optimum' bears scrutiny.

Just wondering.

-- 
John Brownlow
http://www.pinkheadedbug.com