Wonderful explanation, Claus. Many thanks.
So it sounds like I should 301 everything.
One small tactical question...if a page on site B does not have a "good match" on site A -- in the case where a product on site B is not being sold on site A, for example -- where should I 301 the page? Should I point the 301 to the site A page that is most similar, or should I point it to the site A domain root?