I, too, have often wondered what kind of speed I would get on the 200 Mbps fibre plan, but not enough to go through changing my plan to try it out.
When I get a suspicious speed test result, I always stop any background processes, and reboot the fibre modem and test again when it has reconnected to the Internet - so the chance of someone/something else using the network is minimised. I've done that in this case and it hasn't changed the download speed beyond 80-85 Mbps.
What are you using to do the speed test?
When I speedtest at speedtest.net I get about 80Mbps. When I speedtest using the Speedtest for windows 10 app It shows 100Mbps. So the app is more accurate.