Maybe 4-5 years ago with data (cold hard data) to support this. Mormonism is the opposite of the rest of the religious world in that we have a positive correlation between devotion and education/wealth. Everyone else (or nearly so) has a negative correlation.

Re: missionary success among the poor - I think that's true in the short term. More poor people will be willin to listen. But long-term devotion is apparently higher among the affluent and educated in our church.