Hi Jonathan,
William Sloper & Susanna Hale are my 4x gt grandparents also

Going backwards with this family I have:
William bap at Rushall 29 Dec 1775 & Susanna bap at Marden 09 Jul 1776, they married 18 Aug 1796 in Marden.
William's parents: James Sloper bap 13 Dec 1746 Market Lavington & Elizabeth Huntley bap 27 Jul 1751 Rushall
James parents: James Sloper bap 13 May 1719 Market Lavington & Jane unknown
I don't seem to have a James Sloper marrying a Mary, but that may be a gap in my research. Though I do have your 3x gt grandmother, Sarah Sloper, marrying William White at Rushall in 1818.
I am descended from William & Susanna's daughter Mary, who married John Davis in Rushall.
Does that help or confuse?..lol
Regards, Sue