http://pentax-memo.brassworks.jp/
(in Japanese)
This Pentax user/fan has many of the latest Pentax bodies and more importantly many excellent K-mount lenses including the original Pentax ones and those Carl Zeiss ZK lenses built by Cosina. Have a look on those samples that are grouped by lens or camera model and you will not be disappointed. Full samples are available for some.
In addition, he also writes a review for each of his gear for its pros and cons and an overall mark of his is given. Go find out yourself for which lens received a full mark of 120 according to his marking system.
Related:-
A Japanese Pentax Gear Photo Page
Zeiss Stopped Production of (Z)K-mount Lenses
All Voigtlander K-A Mount Lenses are Discontinued