As far as hardness levels, the carbon steel blades are said to be a point or two higher on the Rockwel scale than the stainless blades.
All per Ragnar's site: http://www.ragweedforge.com/SwedishKnifeCatalog.html
Yes Ragnar has very recently updated this page with the merge of the two brands.
However in the old text when these where two different companies he stated that beside the carbon/stainless/laminated differences the rc of the Eriksson was overal a bit higher than Frosts.
I could be wrong because I'm no expert, but this is what I remember.
I still wonder why the clipper series is much more popular than the 9xx and 7xx.
In any case the Eriksson 9xx series are (among others) discontinued according to their website:
http://www.moraofsweden.se/index.php
Also the Frosts 7xx (craftsman) and the Eriksson 5xx series