RF 50 is alright.

However, the higher your level/damage, try dialing it down to maybe RF10-15.
At AR56 and lvl90 weapons, no need to go past RF30, because it one-hits anyone already without multiple phase.
More is not advised as it can cause ping/lag spikes.
Some report good usage with even RF10. Also, when using Swirl (Kazuha, Sucrose, and Venti specifically), RF50 will cause >500ms ping spike when hitting hydro slimes and can cause disconnection/crash.
Take note that with RF active, some skills are possible not dealing damage. One example is Xiao's E, which loses damage.