I was having problems getting the windows 10 preview on my 928. I was trying to upgrade from 8.1 denim. About 75% into the spinning gears it would just stop and an error message 8000010020 or something would appear. I tried several times, clearing space, etc.
After reading suggestions, I did a hard reset, wiping my device. It bricked the phone...spinning gears endless loop.
I used the windows phone recovery tool and it successfully put basic windows 8 on.
I did not choose the old backup to restore during the login process. I wanted it to remain clean.
I also chose not to sync my settings since I did not want it to overwrite the good backup.
I then installed windows insider and set it to Fast track.
When I ran windows update, It put on windows 8.1. It did another 8.1 update after that.
Eventually, it went and got 100166. That was successful!
I did not elect to restore a backup at this point because I wanted to make sure it stayed clean.
Then it went and got 100512. That was also successful.
At this point, I did another Hard reset, so that I could see the restore from backup option during login process.
I chose the old backup image.
After going through settings, going to the store, setting up photos, one drive, etc. it all seems pretty cool so far.
I'm running into some of the typical bugs but I think this going to work as my daily driver.
Hope this helps some other 928 users out there.