Adding my own anecdote, there seems to be some kind of problem with high I/O loads on High Sierra.

One of my projects involves indexing thousands of URLs. During development I use a large (80GB+) local cache of a few million files. Running the cache code (~100 lines of simple Golang) totally brings my iMac (3.8GHz Core i5, 24GB) to its knees. CPU shows as mostly idle & memory pressure is low, yet the machine can't redraw windows properly after about 5GB of I/O to local SSD.

Completely frustrating. I moved the code over to an older (2010!) Mac running Ubuntu and it handles it without breaking a sweat.