My guild raid last night was about 22-24 players and fps was a steady 144 which matches my monitor refresh rate.
Something else I forget to mention. My monitor resolution is set to 2560x1440. The game resolution is set to 3840x2160 @ 66% render scale. This brings it back 2560x1440. This produces a really crisp image. Crisper than when set to 2560x1440 @ 100%