I've been focusing on an engineering career, but now I want to add an MBA. What range of schools should I shoot for: Top 5, 10, 20...?

-GMAT: 670
-Grad School: Masters in Mechanical Engineering, 3.8 GPA, Top 15 school
-Undergrad: Mechanical Engineering, 4.0 GPA, Valedictorian at Top 30 school

-18 months work experience as a Design Engineer
-14 months working as a Research Assistant during grad school by the time I apply (I don't even know if this is worth anything to business schools)

My dream school would be Duke.

Thanks for the help.