I am using the base iMac Pro model (8core/32/1TB/Vega56).
I don't use video apps. But for editing RAWs in Photoshop/Lightroom, the speed of Lightroom isn't that different from my previous iMac (2015, i5 3.3, 32GB, 2 TB Fusion). The Lightroom is laggy for interactive use (culling photo, zooming in/out, retouching, applying filters) and faster hardware won't improve that.
Obviously, there is significant speed improvement when importing, applying batch operation, exporting and pano/HDR merging, so if you need to speed up that part of your workflow it could make sense.
I am still happy with the machine as next to RAW editing I am using it also for software development where it shines.