Try checking eBay "completed listings" to see what these models have sold for on eBay. (Only green prices indicate actual sales; red prices are asking prices for machines that didn't sell at that price.) Some of the descriptions on eBay will likely give you additional information about each model too.
You can also check
http://www.patternreview.com under "sergers/sm". You have to create an ID to view all of the older reviews; well worth doing. You will need to enter Bernina under sergers/sm and then look through all of the Bernina listings for the models you are interested in to find the individual reviews.