You might also want to check out
Superman at Fifty: The Persistence of a Legend. It has an interesting essay on the early days of Siegel and Shuster. Ebay might have a cheap copy. The book is well worth having.
Also check Ebay for the issue of
Time Magazinethat came out in 1988 around the time of Superman's fiftieth anniversary. You might be able to find a copy of the article at the local library depending on how they keep their periodicals.
If you are looking for a good article on Philip Wylie's Gladiator check out Roy Thomas' magazine
Alter Ego # 37 from June 2004. You can probably still get the issue directly from TwoMorrows at their website
http://www.twomorrows.com