DG FIA is a much more powerful post. Just to give you an idea, spend a day with AD FIA (Economic Crime Wing) and ASP of your local area. You will get to know the difference in power/PR/Contacts. Similarly as someone else said above, FIA is federal 'police' with jurisdiction all over the country. Director FIA Lahore wont need permission from Director Karachi to arrest someone in karachi. A SSP Lahore on the other hand would request SSP karachi to arrest someone and will have to follow proper procedure etc. Also police usually deals with lowest strata of criminals such as murderers/kidnappers/rapists etc while FIA deals with white collar crimes. A typical AD FIA would be investigating cases against MNAs/MPAs/Directors of Federal and provincial organizations/bank managers and presidents etc