I'm on one of the last i9 27" imacs. It's a great machine but the timing was unfortunate in that it's just a matter of time before I'm told that Logic updates will be for Silicon machines only.
The 27" is a beautiful all-in-one thing and as has already been mentioned, I wouldn't want to go to 24"
Given your comment, David, what would you do next if you had to buy a new Mac?
Jim