How much evidence provides a conclusive link?

I am a stickler for proof. I do not add individuals to my tree unless I feel I have substantial proof to place them there. I even have a "test" tree where I place individuals that don't have quite the provenance to belong to my family. A bit much, perhaps, but if I don't get it right (or pretty damn close) who will?

Charles M. Webb is one such ancestor...or rather, his parents are. I have conclusive proof that Charles M. Webb is my 5th great-grandfather. I have a copy of his probate documents from Shelby County, Indiana that clearly list his children as Jesse M. Webb, Rene M. Webb, Charles M. Webb (my 4th great-grandfather) and James W. Webb. Charles M. Webb, Sr., died in 1845 and Gerrard Spurrier was named as guardian for his minor children.

One paragraph in Charles Webb's probate documents references monies earned from the sale of four slaves, a woman and three children, in Orange County, Virginia. The slaves were part of the estate of Mary Webb. Charles inherited the monies from the sale of the slaves, but being deceased the money was added to the trust of his minor children. There is no further mention of Mary Webb, except for that she lived in Orange County, Virginia. She is obviously a relative of Charles Webb, but how are they related?

Once they grew to adulthood, the Webb children moved to Ray County, Missouri. I have in my possession a letter to Rene M. Webb in Richmond, Missouri, from William C. Moorson, dated November 16, 1858. The letter is postmarked from Orange, Virginia, and tells Rene Webb that his uncle Jesse has passed away. The letter goes on to state that B.B. Almond was in the process of refuting Uncle Jesse's will on the grounds that he was not in his right mind. The letter's author, William Moorson, lists several witnesses that were willing to state Uncle Jesse was indeed "sane" and indicates that Rene knows the gentlemen:

It states: "I think you and your brother Jesse and Mr. Spurrier were acquainted with William M. Reynolds and James B. Moore." I believe this to be proof that Charles M. Webb, Sr., had a brother Jesse living in Orange County, Virginia.

I was able to find a Jesse M. Webb living with a Mary Webb in Orange County, Virginia on the 1850 census.

This Jesse would be an appropriate age to be a sibling of my Charles M. Webb. Note that Mary would more than likely be his mother and that her property is valued at $990. Quite a large sum for the time.

Are these my Webbs of Orange County, Virginia? I have not yet tried to locate the probate documents for the Mary Webb listed in Charles Webb's estate, so I do not have proof via court documents. But what if there is no proof of her connection? Is the above enough proof? Not for me...what are your thoughts?