The following are lens review sites that I read. I found all of them are useful and their tests are of good reference values in certain areas. If you like to measurbate and compare endlessly before you buy (or just like me doing endless measurbations after the purchase! ;=>), go to explore those sites with plenty of your valuable time in your life! ;-D (Well, just don't blame me for wasting your time in your life afterwards or when you grow old and look back! :-))
1. SLR Gear.com (by the Imaging Resource)
Main Page: http://www.slrgear.com/reviews/index.php
Pentax Page: http://www.slrgear.com/reviews/showcat.php/cat/44
2. PhotoZone
Main Page: http://www.photozone.de/reviews
Pentax Page: http://www.photozone.de/Reviews/overview#pentax
3. Dpreview
Main Page: http://www.dpreview.com/lensreviews/
Pentax Page: No Pentax Page (nor for any other brands as well, anyway)
4. LensTip.com (English translated reports, tests originally by the Polish Optyczne.pl)
Main Page: http://lenstip.com/lenses_reviews.html
Pentax Page: http://lenstip.com/index.html?test=obiektywu&producent=13&model=&typ=0&moc=0&przetest=1&szukaj=Search
Do note that for most of the time absolute figures should not be compared across different testing systems of different review sites, but in contrast the overall results could be. After all, the exact figures should be compared amongst each others with the same "ruler" for measurement, i.e. amongst the tests done by the same site (and with the same DSLR body). For example, the distortion figures in percentage could be much different for the same lens model under different tests, but if you are to compare the test figures of other lens models within the same testing system/procedures, you would probably be able to draw similar conclusions on the strengths and weaknesses of a particular lens, relatively speaking, even though you are to do a similar comparison for other lenses that you are interested in at another review site(s).
Enjoy!