How fast can a stock leaf rearend be?

there are a few things to consider also when you talk about factory rear suspension...
these where mass production parts.
so mounting points are gonna be in a range.....
some guys get lucky with the architecture of there cars..."pot luck"
if your planning on using stock rear end set up..it wont cost you anything to measure it and index the mounting points...making them square to the front tracking..
this will greatly improve you chances of getting the car to hook ...
i run 6.67 et with 1.39 60ft on ss springs an 8.75 housing (mark williams billet internals) a gusseted pinion snubber (adjustible) and $9.00 monroe shocks..
with a 10wx28 mt slick.
we had to shim the rear to get it straight..and set up the rear shackles for free movement (swing)....
you can launch and run my car with no hands on the steering wheel.
cheapst