I'm a bit confused about your question. If you can trace your patriline back to a Madge who married in 1695 why do you have a query about a baptism in 1718? Or are you saying that this baptism is on your father's side of the family but not on the patriline? Y-DNA only works for the direct fatherline as the Y-chromosome is passed down in all-male line from father to son. An autosomal DNA is best used for finding connections within the last five or six generations. It will give you matches on all of your family lines on both your mother's and father's sides, including the patriline. However, because autosomal DNA is diluted with each passing generation, the test is best used for finding matches within the last five or six generations. It's quite likely that you have not inherited any DNA from your Madge ancestors in the 1600s and early 1700s.
Please feel free to take advantage of the free transfer to add your AncestryDNA results to the Devon Project. You are likely to get some matches who are not in the Ancestry database.
If you want to explore your deep Madge ancestry then you would need to take a 37-marker Y-DNA test. However, I don't currently have anyone with the Madge surname in the Devon Project so the test might not help you that much at present. There is a Madge DNA Project you could join in addition to the Devon Project though it
currently only has six participants: