Article that does some graphics comparing different years from 1896 to 2008
http://www.slate.com/articles/sports/fivering_circus/2012/07/olympics_interactive_how_would_the_champs_of_bygone_olympics_fare_against_today_s_best_sprinters_jumpers_throwers_and_swimmers_.html
Many of the events (except swimming) have pretty much leveled off. "Womens" discus have dropped dramatically since drug testing has come about.