I’ve just updated my BIOS, made sure that everything was at defaults (didn’t touch Ai Suite either) and rebuilt UE4 again.
Total build time: 1491.19 seconds (Local executor: 1377.77 seconds) 24.85 mins | 22.96 mins
Going to try the 3.5Ghz again, this time from Ryzen Master.
EDIT for 3.5Ghz:
Total build time: 1367.24 seconds (Local executor: 1258.25 seconds) 22.78 mins | 20.97 mins
Wish I could remember what I changed in the BIOS when I first set up the PC.
I’ll give that Lightroom: Interior Day Light scene a go too.