I have not found that sarah tubb's line goes back to the Mayflower. Re Wiliam Tubbs and Mercy Sprague:
"William married, probably at Duxbury, 9 Nov. 1637 Mercy Sprague, born probably in England ca. 1620; living in RI July 1668; daughter of Francis. With her parents she arrived at Plymouth in July 1623 on the vessel "Ann", the third to land at Plymouth. (Savage says; Francis Sprague, wife and one daughter came on Ann. At division of cattle in 1627, Mercey and Ann were his only named children. Francis was living in 1666.) The Spragues lived at Plymouth until ca. 1631-2 when Francis was among the early settlers of Duxbury. William also settled there for in all records following his marriage, he is given as a resident of Duxbury."
I do have a Mayflower ancestor in the Wilson line.