Row 5 is two and two 5AB EF, row 6 is two and three 6AB 6DEF in equipment that hasn't gotten "economy comfort". Other than row 5, every "E" seat is a middle for the older non "EC" equipment.

If the equipment does have Economy comfort, as most do now, row 5 doesn't exist, and row 6 is the two and two 6AB EF and then row 7 goes to two and three AB DEF.

According to Delta's website, all two class planes have economy comfort now as of June 7th. The DC9-50 lost row 5 to accommodate EC.

Beginning June 7th you can enjoy Economy Comfort™ on all two-class Delta flights worldwide. With greater legroom, more recline on select routes, and other premium features, Delta has taken affordable comfort to new heights. Recline up to 50% more on select flights Three to four inches (7-10 cm) additional legroom. Complimentary beer, spirits & wine on select international flights