8 Gray x 5 fractions is my usual SBRT approach to an intact prostate primary, and the published series out of UCLA and elsewhere show >90% control rates. The same dose is very tolerable in the lung unless ultra central. I would try to get the ITV dose up to 50 Gy+, but not necessarily the whole P...

No reason not to go with standard >100 BED approaches (54/3, 48-50/4, 50/5, 60/8), as we don't necessarily have prospective data for prostate cancer specifically.