I know this is old, but I just came across it and noticed that you did not get a reply. I have researched the family name for years and have found many interesting variations on the spelling (since only in recent decades have most people been particularly concerned about it). Your Irish Sagriff is a new one on me, however.
It reminds me of the branch of the family that settled in eastern Kentucky from the North Carolina branch. One group of them during the 19th Century started spelling the name Sagraves and their descendants still do.
Since there is a large Irish contingent of the Seagrave family, mostly descended from Englishmen who migrated there in the 12th and 13th Centuries, it is very possible that your Sagriff is a misunderstanding of the name. Generally in earlier times only the small portion of the population that was literate (priests, clerks, scribes, etc.) wrote down names as he thought they should be spelled, causing no end of trouble for modern researchers.
For a detailed discussion of the original English baronial family that had many Irish connections, see the book "The Seagrave Family 1066-1935" by Charles W. Seagrave, London, 1936. It is only available in major libraries now, including the Genealogy Library in Salt Lake City.