Most of that information is about persecution of Jews during the Medieval period. There's some indication of small Jewish settlements in France and the Rhineland, but Jews don't seem to have been nearly as common in those areas as in Poland and Russia, at least not until the late Medieval period. And the fact that at least some of the Polish Jews spoke a dialect based partly on German certainly doesn't limit their origin point to somewhere within the boundaries of present day Germany. There were a lot of German speaking people in Eastern Europe until after WWII. I still think that most European Jews are descended from Jews who migrated from the Middle East north into Russia, then gradually moved west.
I probably wasn't clear about it, but the links to the sites about the persecutions were mainly to support the hypothesis that the "genetic bottleneck" which affected the Ashkenazim but not the Sephardim could have taken place at this time and in this location. It's a good fit for it genetically, because the bottleneck has been estimated to have taken place around 1000 AD if I remember correctly. The articles also serve to show the number of Jewish communities that existed from 800 AD in this area. However, I also provided other links.
There's also this from Medieval Germany: An Encyclopedia, Edited by John M. Jeep, a google book:
"In the ninth century there were only a few dozen Jewish families in Germany, probably a few hundred in the tenth century. It has been estimated that there were as many as 4,000 to 5,000 Jews by the end of the tenth century, and 20,000 to 25,000 Jews by the end of the eleventh century..."
http://books.google.com/books?id=p4...l Jewish communities in the Rhineland&f=false
Now, I'm always a little leery about population figures from this period, but I think it might be safe to say that there were a substantial number of Jews in the Rhineland and neighboring areas of France by the end of the eleventh century even if you halve the figures.
(There were also substantial communities in Italy, and France outside of Alsace, and Spain at the time. The Italian communities remained relatively undisturbed, but the French Jews were expelled in 1394, although there had been numerous expulsions and recalls since the beginning of the 1000's. They had to go somewhere; there is no indication that they all converted, and there's no indication that they went to Muslim lands. At least, I'm not aware of any. There are also the even better known expulsions involving the Spanish Jews, although in that case a high percentage of them went to North Africa or to regions ruled by Muslims and form the basis for the Sephardic communities. (and perhaps even to the New World. There's the case of the converso element in southwestern American "Hispanics" for example.) Even when they went to the Netherlands, they maintained their separate ritual and the use of Ladino, and seem to have practiced a great degree of endogamy even with regard to the Ashkenaz, a term meaning German Jew by the way.)
Now, this isn't to say that some Jews didn't return after the various "pogroms", because there is every indication they did. After the first crusade, for instance, there seems to have been an establishment of very small dispersed communities in the Rhineland, although they greatly diminish after the progroms surrounding the Black Death. This is a map of the Jewish communities, all small, from 1349 in the area of the Rhineland:
http://pages.uoregon.edu/dluebke/Reformations441/JewishCommunities1349.html
Then there's this from the Jewish Virtual Library linked to above:
There is no specific date that marks Jewish immigration to Poland. A journal account of Ibrahim ibn Jakub, a Jewish traveler, merchant and diplomat from Spain mentions
Cracow and the First Duke of Poland, Mieszko I. More Jews arrived during the period of the first Crusade in 1098, while leaving persecution in Bohemia, according to the Chronicler of Prague. There is also archeological evidence, coins from the period with inscriptions in Hebrew, revealing that other Jewish merchants traveled to Poland in the 12
th century. The coins may have belonged to 12
th century Jewish traders,
Holekhei Rusyah (travelers to Russia).
While persecution took place across Europe during the
Crusades, in the 13
th century, Poland served as a haven for European Jewry because of its relative tolerance. During this period, Poland began its colonization process. It suffered great losses from Mongol invasions in 1241 and therefore encouraged Jewish immigrants to settle the towns and villages. Immigrants flocked to Poland from Bohemia-Moravia, Germany, Italy, Spain and colonies in the Crimea. No central authority could stop the immigration. Refugees from Germany brought with them German and Hebrew dialects that eventually became Yiddish.
Now, I'm aware of the criticism of this theory from Jits Van Straten, but I didn't find it very convincing. The fact is that while the contemporaneous fragments we have from Jewish sources often indicate movement by the survivors to other "German" areas, some of those areas were indeed to the east, and some are in areas that are now part of Poland. I don't think the fact that these people didn't immediately make a beeline for Poland necessarily means that there wasn't a gradual movement east that was accelerated every time there was another persecution, especially given the favorable climate for them in the Poland of that time. Of course, it's far from a settled matter given that we don't have specific documentary evidence of the establishment of these kinds of communities in Poland by the exiles.
http://www.mankindquarterly.org/samples/vanStratenJewishMigrations.pdf
Also, when I said I had looked for documentation of the existence of any signficant Jewish settlements in Poland or the Ukraine before, say, 1000 AD, and the proposed movements of Jewish exiles from the west, I was specifically thinking of this Van Straten article. I thought perhaps he would include such data, but he advances no alternative hypothesis to explain the presence of Jewish communities in Poland.
In that regard, have you found documentary evidence of such settlements? There is that teasing reference above to Crimean Jews also moving to Poland, but that's the only thing I've ever seen, and there's no citation for it. I'm not playing gotcha here, as I hope you realize. I've looked, and I've never found any. Certainly, data like that would have to be factored into the equation.
I do also now get how your hypothesis differs from the "Khazarian" one.