How fast can a stock leaf rearend be?

My '70 duster with the 416 stroker,ran consistent low 6.90's 1/8 11.0's 1/4,with 60's in the low 1.40's,using just heayduty leafs pinion snubber and cheap drag shocks so basically stock setup..wheel/wheels up every launch..:-D,there are some cars out there well into the 9's on leaf springs..