It is often useful to test with a test variation server on official builds, since testing at TOT is often not representative if an experiment is going out on another channel.

However, in cases where the version you are trying to test is not released yet (for instance the next stable release), the next best thing is one channel below (e.g. testing on beta M64 in preparation for M64 stable launch).

In this particular scenario, it would be ideal to pass --fake-variations-channel=stable to the official M64 beta build, to simulate as close to reality as possible what a stable M64 launch would look like.