Getting your DNA tested with FamilyTreeDNA will have your results compared to over 80,000 other project participant's results. If you match results with another participant, you may be lucky to find that person has a paper trail further back than you have. They may have had access to a family bible that no one else knew existed. Of course, I would suspect that if a DNA match occurs, it will happen with another person in your surname group, unless there has been an adoption along the way. Not everyone posts their tree on-line, but they may join a DNA project. There are others that have posted their trees with errors they are unaware of, then hooked up with another "relative" who posted their tree, then found out through DNA testing that they were not related, and that they had those errors in their tree. You may have an ancestor who came to the US from
England, but he never reported from where in
England. A fellow DNA project member you match might have an ancestor who did report from where in
England that he came from.