If I factory reset my phone, will it downgrade me to back to IOS 10.3?

Last weekend I decided that I wanted to upgrade my iPhone six plus to IOS 11 beta, and before I did so, I backed my IPhone up on Itunes. Now I want to downgrade back to IOS 10.3 since the actual update is coming out this week, however the computer I backed my IPhone up on is not functioning properly. I was wondering if I logged into my ITunes account on another computer, would my files be there, or if I just factory reset my phone alone will I downgrade back to IOS 10.3 and just have to deal with losing everything?

No doing a factory reset will not 'downgrade' you back. There's no way to downgrade; and if there's, Apple usually fixes that very, very quickly.

Your backups in iTunes are stored on that computer, so if you use a new computer, the backups will not be there.

If you used iCloud to backup your files, then you should be fine, but if you didn't, you're out of luck.

If firmware has been updated then it is what it is. It won't revert back unless you do the rollback yourself

Well since it is coming out tomorrow you could just wait & update to that & be fine. Kinda makes no sense to go back to iOS 10.3.3 only to go back to iOS 11 in a couple of hours.

If what you said is accurate as far as backing up to a computer, but it not functional at this point, then no signing in elsewhere wouldn't do anything since the backup is stored on the other computer, not any other.

Yes, factory resetting would get you back down to iOS 10 but again with it being released very soon (almost less than a day) may as well just wait for it & update & continue from there.

You will still get the actual ios11 upgrade, and there's no good way to downgrade without third party programs, as even if you factory restore the phone, it will still retain the last software version that was loaded

Not at all