Roughly 3 years ago I made a benchmark save with 10000 colonists. I measured performance and stored the results. I thought about it today and ran some new tests, with my new pc and rimworld 1.4 as new additions. I have also made the save available again. If you like you can run the benchmark yourself and submit the results in the comments.
Important note: run it with core only and try to be accurate with the timing. Make sure you read the RandyMe.txt file.