Yes, when I've got my gold iPhone 6Plus 128 gb unlocked in September I did experience constant rebooting and red screen after restoring from the most recent backup of my previous iPhone 5S 64 GB via beta iTunes12.0.
I was unable to put this phone in recovery mode on my iMac 27" 2009, beta Yosemite OS X. After 7 unsuccessful attempts I've had to call Apple Care and ultimately I did talk to senior Apple software engineer for about 2 hours. He had basically to download and execute special diagnostic software on my iMac in order to make exact snapshot of my system. Then I've uploaded this information to specially provided link he gave me.He told me it will take at least 48 hours or more to analyze this file by Apple development team. I wasn't even able to turn it off no matter what I've tried. I thought I would have to spend time to go Apple store and replace it right away so frustrated I was.
Then, all of a sudden I've decided to put in recovery mode on my other computer MacPro 2008, OS X Mavericks, iTunes 11.1.1. Wow, there was immediate success-I was able to put my new phone in the recovery mode, then restored it to the factory default and this issue was completely resolved. I did another fresh backup of my old iPhone 5S to iMac 2009 and restored my new iPhone 6 Plus 128 gb to this backup on the same iMac 2009 with beta Yosemite and beta iTunes 12.0. Since then and till now I've never experienced any issues with everything, considering my staggering amount of applications(about 400) plus 10 gb audio files and about 20 gb of movies on my iPhone. Of course, I've shared my experience next day with aforementioned senior Apple engineer. I'm pretty sure now there was more software issue rather than hardware issue. I hope my story will help you to make a right decision if are in doubt whether to exchange it or not.
