I was interested in the bokeh my M lenses produce. I decided to shoot a test, as I understand bokeh improves stopping down from max aperture as it gets rid of the ugly condom ring effect. Lenses run in the Picasa slideshow as follows 3.5/28, 2.8/40, 1.7/50, 2/85, 3.5/135, 4/200, 75-150.
What was interesting, was shooting a high contrast subject and keeping the subject the same size by always shooting at a distance equal to 20x focal length away from the subject (roughly, using a tape measure to the k-mount).
The quantity that really improves when stopping down is the longitudinal colour fringing. When I have more time, I will post crops. For now its the whole image, which is more representative of the details you would see in a photo in any case. I'm also getting to like the 200mm as a portrait lens.
Picasa Web Albums - hoojammyflip - lens testing