first of all my excuses to everyone when I did not reply to your E-Mails. Unfortunately I had a busy 2006.
Meanwhile I have a photo of an old family tree from my great-grandfather. I have taken a photo from it and created a PDF. In the PDF I have drawn boxes and typed in the handwritings. Please note that some writings were difficult to read.
This is my personal direct line (going back in time):
Stefan Gentz (*1975) Beatrice Gentz (*1952) Wulfrin Sigurd Gentz (1929-1990) Carl Ludwig Erich Gentz (1888-1957) Johann Heinrich (1839-1902) David Ludwig Gentz (1810-1858) Johann Heinrich Gentz (1773-1839) Friedrich Gentz (1743-1797) Johannes (Hans) Gentz 1706-1774) Hermann Gentz (16??-1719)
The whole tree is pretty big and maybe you can find a link to your family: