Obviously, the spellings of this surname vary, and so do the y-dna test results. Not all of these families descend from the same most distant y-dna ancestor.  Acknowledging those realities, the goal of this project is to use y-chromosome dna test results to help Gist, Gest, Guess, Guest, etc., families trace their paternal lines as far back as possible to their actual biological (rather than imaginary) ancestors.

The standard work on the family in North America is Christopher Gist of Maryland and Some of His Descendants: 1679-1957, by Jean Muir Dorsey and Maxwell Jay Dorsey. It is well researched and documented. Buy a copy of it if you can. 

Regarding genealogy and the Gist book mentioned above, please don't jump over centuries of time and list the immigrants, Christopher Gist and his wife, Edith Cromwell, as your most distant known ancestors unless you have a very good paper trail to them supported in the book, or you have an extremely close y-dna test match to someone who does, via both STRs (Short Tandem Repeats) and SNP testing (such as FTDNA's Big Y-700). Not everyone with the Gist, Gest, Guess, Guest surname is descended from Christopher and Edith. It would be nice if they were, but they aren't. Far better to use dna testing to find your true ancestors than to claim the wrong ancestors and contribute to ongoing genealogical confusion.

So, please, claim ancestors only as far back as you can support the claim with solid documentation and/or dna evidence.