To be honest, I think the Olmstead book has been pretty much superceded by the enormous wave of research on Achaemenid Persia of the past 30 years. The best short introduction to the subject is Josef Wiesehofer's "Ancient Persia" - the definitive and indeed exhaustive text is Pierre Briant's "From Cyrus to Alexander: A History of the Persian Empire". One Achaemenidist actually complained to me that Briant had left her nothing to write about!