My longest read novel is "Shogun" by James Clavell at1245pp, followed by "The Journeyer" by Gary Jennings at 1219pp.
And my longest unread are "Harlot's Ghost" by Norman Mailer at 1374pp and "Whirlwind" by James Clavell at 1343pp. The latter was bought for me as a birthday present by a friend who'd seen me reading "Shogun" and not bothered to ask if I liked it. To make matters worse he'd also been considering buying me "It" but plumped for the Clavell as he hadn't seen me reading any King
I have "Battlefield Earth" somewhere, but have never got around to that one either.