Instructions to revert back to iOS 8 for iPhone 6 and 6+
Download
iPhone 6+ - http://appldnld.apple.com/iOS8/031-05555.20140917.YWW0v/iPhone7,1_8.0_12A366_Res tore.ipsw
iPhone 6 - http://appldnld.apple.com/iOS8/031-05647.20140917.b0n9s/iPhone7,2_8.0_12A365_Res tore.ipsw
Download may take a while as everyone is downloading it right now
Once downloaded, move the file to the desktop (or wherever, just makes it easier to find)
Open iTunes
Just to be safe...do a backup and save it to your computer. Click "Back Up Now"
Connect iPhone to Computer
On Mac : While holding alt/option click on "Check For Updates". Finder will open up, navigate to the desktop and click on the ipsw file (that you just downloaded) and follow the promptings. Takes 2-3 minutes with one reboot.
I just did this, works perfectly.