Ensuring consistency and minimal interference during benchmarking?
Items you've considered are already good! Disabling internet stops lot of stray processes.
You can try Safe mode to do the tests if they don't need the services disabled in that mode. Also consider making a new user account for doing the testing.
https://support.apple.com/HT201262

Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed.

That's the closest you can get to a brand new Mac.
Also, if the tests' results use huge storage, its best to delete them after every run since remaining storage also affects VM usage and increases memory pressure.