I finally was able to get iTunes to start the iOS 8 download on my Air. Estimated time was 30 minutes at first, then kept slowing down eventually went to 80 minutes. So I browsed iClarified and they've posted the direct links to every iOS 8 update file. Don't worry, the .ipsw is downloaded directly from Apple server. I downloaded both the iPad Air and rMini .ipsw files, 2GB each, less than 10 minutes. Placed the .ipsw file in the iPad Software Updates folder for iTunes, done. Link to iPad .ipsw here. iPhone here.