Yeah, if I do a firmware update I always do a factory reset in the recovery menu. Then after the update is finished and optimized, I do a wipe cache partition in the recovery menu. I then set it up like a new device, bring over very little that I have backed up, mainly sms, and Nova settings.
I am closing this thread -- Please use the thread below to discuss about Android M for the Nexus 6. This way we won't have too many threads open on the subject.