In trying to answer this question I discovered the research  done by Admission Consultants in the USA. MBA  Ranking and ROI has been debated for a long time. This study gives a guide to answer this question. But do not take it as truly independent. Admission Consultants do make their money by getting students into top schools. Graphs and a text version can be found here.

The results do indicate that top schools in the USA do earn up to 20% more than other business schools. And there are quite a difference between the top ranked school and the 31st ranked school. Some regional differences were also discovered.

Included is the Video indicating the results.

MBA  ROI Study: Measuring Brand Name Value of Top Business Schools