I know the PRA wants to build a database of interesting websites that mention Penningtons in history. This is a very good one: "Catalogue of Papers of William Henry Cavendish Bentinck, 3rd Duke of Portland". If you got to http://mss.nott.ac.uk/cats/port_3rdduke15cat.html#top and search the page with the edit toolbar you will find many interesting letters from assorted well-to-do Penningtons to the Duke.