I had posted my Lightroom experience in a different thread before:
I went for the 10 core, 64, 1 TB, Vega 64 system. My old system was a 6 core i7 Windows based machine which was slightly faster than my MacBook 13" i5 from 2015.
In January when I migrated I run a test with 727 RAW files. I loaded them onto the same empty catalog with a wiped preview cache sitting on an SSD. I loaded and copied the images and created 1:1 previews in parallel.
Windows i7 6 core: 42 minutes, 37 seconds
iMac Pro: 10 minutes, 33 seconds
Regarding how much LR benefits from multiple cores. Here is a screen print I took from the Activity Monitor during above import:
View attachment 751311
While some felt that LR prior 7.2 wouldn't support more than 4 to 6 cores, my experience was different. Would be interesting to see how this looks on a 18 core machine.
Approx. 2 weeks ago I came home from a shoot with 2,300 images. It's amazing how the iMac Pro is processing them. Best of all, after the first 20 photos are loaded, I can start working and make my first run to discard those which are not tack sharp.
This was basically not possible on the old machine due to the lag moving from photo to photo. I had to wait for 2 to 3 hours until the job was completely loaded and rendered before I could make my first run.
On the iMac Pro this is easy while the system stays quiet and I can't hear the fan.
The above was prior 7.2 which should still give you an indication. With 7.2 during edit it feels like slightly faster. I haven't had a large import/preview job since I am on 7.2.