The Twentse Vogelwerkgroep test reports are interesting but written in Dutch (funnily enough!).
Fortunatly
http://translate.google.com
does translate Dutch (and a lot of other languages) into English with varying amounts of fidelity. You get a lot more out of the site with it's help!
Unfortunatly the site is not well set up to help google do the translation
Try this translated listing of the test report virtual directory
http://translate.google.com/transla.../testrapporten/
And pick a folder of interest.
The translation is not great but good enough.