I'm not sure of the equations, but I have heard that a softball being pitched at 60 MPH from 40 feet is like a baseball being pitched 100 MPH from where ever they pitch from

Here's my shot at this:
SB@40 ft BB@60 ft
40 = 60 mph
50 = 75 mph
60 = 90 mph
70 = 100+

This is assuming that the distance traveled is from rubber to plate. I believe that girls who use a leap-style pitch can add about 3-5 mph in perceived reaction time depending how far they leap.

From 30 ft:
40 = 80 mph
50 = 100
60 = 120?

The numbers really make a case for starting kids at the beginning with a leap-style pitch. Not only are they throwing harder due to the more efficient mechanical advantage, but they're closer--shortening the batter's reaction time.