I know of at least four eminent historians who write out their research on either 4×6 or 5×8 notecards. I have interviewed both James McPherson and Allen Guelzo. I have read a Gordon Wood book. I plan to read Ron Chernow in the near future. Here Chernow says that he made 25,000 4×6 cards before writing his latest tome on Mark Twain. You will hear about it in the first two minutes.