Ok - I figured out the problem. For some reason MSI afterburner was not following my custom fan profile and was setting the fan at 0% (that's right - no fan). It was when I was messing with different settings that I accidentally turned off user fan profiles and heard the fan switch on.
Temperatures are at 72C at 1950 Core / 7752 Mem / 100% fan
Thanks for your help.
i5-8600K CPU @ 3.60GHz, 32GB DDR4 3200, Zotac RTX 2080 TwinFan, ASUS XG35V 3440 x 1440 (32 bit) (100Hz), 1TB Evo 960 NVME M.2, 500GB 850 Evo SSD, 1 TB 970 Pro NVME M.2, 2TB WD Blue, 8TB WD MyBook