I've detailed this abit in my "Eternal Blue Sky" TL, basicly cut off from Persia thanks to the invasion of the Tengriists, Islam absorbs the Hellenism from Syria, the Levent,North Africa and Egypt where now they have a very large majority of Orthodox and Copt Christians amongst their peoples -unlike if they had Persia where most would eventually convert to Islam- so the influence by Hellenistic society would probably back up a Islamic Golden Age-tred much longer then OTL and somewhat democratic (over blood line) in choosing the Caliph, as well as a Hellenistic inspired mystical Sufi deveriation when you get into some elements of the East Church's doctrine.