Taking a more scientic tack, I looked at the list of shared books on Library Thing's Historical Fiction group, which has 243 members. Today's results for "Most commonly shared books (weighted)":
Jonathan Strange & Mr Norrell by Susanna Clarke (80), Harry Potter and the sorcerer's stone by J.K. Rowling (95), Harry Potter and the Chamber of Secrets by J.K. Rowling (90), Harry Potter and the goblet of fire by J.K. Rowling (86), Harry Potter and the prisoner of Azkaban by J.K. Rowling (85), Harry Potter and the Order of the Phoenix by J.K. Rowling (86), The hobbit, or, There and back again by J.R.R. Tolkien (76), Girl with a pearl earring by Tracy Chevalier (50), Harry Potter and the Half-Blood Prince by J.K. Rowling (84), The Silmarillion by J.R.R. Tolkien (60)
When I looked for historical fiction on my own shelf that I share with other users, the top novel was Gone With the Wind, shared by 1,081 members. After that, the next shared book in my library was The Crimson Petal and the White, shared by 563 members.
It seems that I have some seriously obscure tastes, for I'm the only person who lists Prophecy for a Queen by Dilys Gater. Also owned only by yours truly are certain novels by Juliet Dymoke, Maureen Peters, Margaret Campbell Barnes, and Brenda Honeyman.
Three very intelligent, discerning people on Library Thing (plus me, of course) have a copy of my own novel. You rock, guys!
Bernard Cornwell's The Winter King is shared by 175 people; only six claim his Crackdown. I expected more people to own Sharon Penman's books: 168 listed Here Be Dragons, while only 39 had Prince of Darkness. She did better than the wildly prolific Jean Plaidy, though: only 52 listed The Lady in the Tower, the top Plaidy book on Library Thing. Of course, some of Plaidy's books appear under different titles, but I was still surprised to see how many of her books were owned by fewer than ten people.
What does all of this prove? (1) it's Sunday and I have some free time on my hands and (2) more readers of historical fiction need to get to Library Thing and get their libraries listed. I bet your shelves are just bulging with Penmans, Plaidys, and even Peters. It's time to come clean about it.