I liked this article about the libraries of CEOs.

"C.E.O. Libraries Reveal Keys to Success

Explore the personal libraries of successful chief executives and discover what makes them think, not compete."

 

However, I don't think Churchill spent 6 years only reading after losing the 1944 general election. It was during this period that he did a lot of writing, in fact (such as has 6 volume history of the second world war).  I have decided that I must read the 7 Pillars of Wisdom; I hope it is out of copyright and therefore available from Project Gutenberg.