Did non-Abrahamic populations like Zoroastrians, Manicheans and Buddhists (as well as the indigenous pantheons of Afghanistan and Central Asia) convert faster than their counterparts, or were they already on the decline?
It took about 200 years to cross the 50% mark. Here is a graph for Iran, which was slightly faster than in other regions under Muslim rule:
http://4.bp.blogspot.com/-69BqAL9ARKg/T1WBF0NwxeI/AAAAAAAAABo/IRxr3nIjSIo/s1600/Bulliet-Iran.gif
Bulliet achieved these results by examining the names which appear in Muslim biographical dictionaries to determine at what point in each family's genealogy they converted to Islam, and was thus able to determine a rough rate of conversion, which essentially corresponds to an S-curve.
Richard W. Bulliet, Conversion to Islam in the Medieval Period: An Essay in Quantitative History (Cambridge: Harvard University Press, 1979), p. 44.
