RE: SAP EHP 3
Between EHP3 SPS3 to SPS13 their would be no change to business functions or application functionality as support packages only deliver code corrections and fixes. New functionality is only brought in when you go to a different EHP level.
If going to a different EHP level, you can use the Business Function Predictor tool to see what changes occur:
see link in middle of page
If changing support package stack level, but remaining on the same EHP level you can generate a side effects report on the SAP service marketplace.
Hope this answers your query.