There’s some affectionate rivalry between two of journalism’s cult heroes, it seems. Page Six hears that Jane Pratt has sold her memoir — but we’re told the Sassy legend said she didn’t care how much it went for, as long as it was more than the memoir of her one-time protege Cat Marnell. We’re told Pratt’s tell-all did indeed fetch more than the half million than Marnell’s beloved “How To Murder Your Life” snagged in 2013. We reported in October that the former XOJane editor was shopping a book that would chronicle, among other things, her time at Conde Nast (including run-ins with Si Newhouse and Anna Wintour), her famous friendships with Courtney Love, Michael Stipe, Chloe Sevigny, Courteney Cox, Drew Barrymore and others, as well as private struggles she has faced. Famed editor Jane Pratt has sold a memoir, Page Six has learned.…