Quote Originally Posted by Prodigal
Also does the conversion still progress while you are laying siege?
Yep. I took a city with a Sassanid all-cavalry stack (starved it out) and when I took the place it was already quite heavily Zoroastrian. The combination of neighbouring provinces and my two family members (with piety virtues and some religious ancillaries) seemed to be pretty effective.

Not something I reccommend though, unless you like taking it slow, or can't be bothered waiting for your siege train stack. :)