This isn't really a bug, but the late game can still be rather laggy. I thought I'd try and help by sending a late game rather laggy file incase more files might still help.
A annoying part of the lag is when dupes stand around for 10 seconds so before they are assigned their next job which is just 1-2 tiles away.
Steps to Reproduce
Just Open the file. As time goes on this slow down dramatically. Dupes eventually stop and wait for nearly 10 seconds before they get assigned jobs.
This issue has not been confirmed by a developer yet.