It's highly unlikely that your Ashkenazi ancestors came from Greater Poland. In the map I linked, you can see the percentage of Jews by Vovoideship in the Interbellum period. Jews formed only 0,5 of the Population, as opposed to the national average of 10%. It wasn't known as an area of traditional Jewish settlement. Much of the ancestors of Greater Poles is either German, Dutch or Flemish. I'm from Greater Poland and my DNA is 23% (only my grandfather is from GP, so most of that is probably from him). My Y chromosome lineage is from the Netherlands (father's father's father, etc.) and looking at my family geneaology, there are virtually only German last-names from the Greater Polish ancestors. Greater Poland was depopulated in the late 1600's, early 1700's by wars with Sweden and various epidemics. It was settled by Bambergers (Bambrzy) who came from Franconia. There was also frequent settlement by Flemish and other Germanic settlers throughout history. This region is characteristically very Germanized (not only because of partitions) and this is evident in our heavily German-based dialect. How much of your DNA is germanic? How far back was your ancestor in Greater Poland? I could help you with any genealogy you'd like to do.