Thanks for your recent input with regards to my question about potentially buying the 5X again! Here are my first two runs with the unit- I am quite happy overall (both with my Stryd);
Especially after installing the UK isles talkytoaster maps (followed the guide on here http://www.activejr.com/how-to-install-full-topo-contour-maps-on-the-garmin-fenix-5x/)
https://connect.garmin.com/modern/activity/1719146803 (still on smart recording, silly me)
https://connect.garmin.com/modern/activity/1722356943 (every second recording)
The only issue that I noticed (I am on the latest beta, is that resting HR only updates once per day and the value has been very unusual over the past two days); all day HR works fine though..
P.S I still intend to keep my FR935 for when GPS accuracy matters, even though I am quite happy with the above.
I also navigated from point A to B to test it out and everything worked well (other than no alerts when you try going off course)