Here's the patternreview page for Jukie reviews:
http://sewing.patternreview.com/cgi-bin/topsearch.pl
You should be able to find reviews of the 600 model there.
Oops! Sorry, that url doesn't work. Just go to
http://www.patternreview.com, select the category of sm/serger, enter Juki, and it will take you to all the Juki reviews. You can see from the title which are reviews of the 600.