For me “Always 3D Clock” is similar to NVIDIA Power management mode/Prefer maximum performance, but NVIDIA maximizes the GPU base clock and memory clock.
Anyway, for me when “Always 3D Clock” is enabled it maximizes the GPU boost clock and memory clock (ensure your GPU overclock is stable before applying).
Always 3D Clock = on.
Always 3D Clock = off (Note: NVIDA maintains set memory clock and defaults to GPU base clock, but not boost clock)
Always 3D Clock =off, NVIDIA Power Management mode/Optimal Power.