Best advice is to stay on the stable public release (so 11.0.3) and restore your backup from there. Will be zero compatibility issues going up.
I’d imagine the iPhone X will ship with 11.1, but nobody other than Apple knows at this point. Stay on 11.0.3 if you haven’t already upgraded. Worst case is you’ll have to update your X to pre-release software.
Yea, I'm not using Beta software on my phone, I was just worried that an old backup might not be compatible with newer software. But Vundu has replied to me to let me know that restoring from an older iOS is ok.
If 11.1 is released today/later this week, I will probably update and then I might have to update the X before restoring.
Thanks for getting back to me!