Technically a speed-bump, but quite a significant one. One YouTuber in his review said not to buy if you already have a 2017 iMac or newer.
Feeling for a couple of friends on the Mac User Group management committee: in the last 6 weeks both have bought high-end 27-inch iMacs, now thoroughly superseded.

I thought I'd compare the cost of a top spec iMac & a low spec iMac Pro, trying to keep things like RAM & drive space as close as possible.
The prices were very close, with the Pro version winning because of the Xenon processors.

matigo.ca.