A recent post
featured the highest-paid high school teachers in Illinois. Here's an update, with a chart above that compares the highest paid high school teachers in Illinois to their highest paid Ph.D. counterparts in the same academic field at the main campus of the University of Illinois (salary database here
In the case of some academic disciplines like English, French, theater and music, it looks there is much greater salary potential for high school teachers with a Master's degree than for college professors with a Ph.D., at least by comparing the highest paid teachers in each system. If I can get average or median salaries for each level of education, I'll make that comparison in the future.