No, I agree with Vibstronium. And I do have such a monitor FWIW.
With V-Sync, the GPU renders frames to fit a fixed schedule, e.g. once every 1/60 second for 60 Hz. If it could render twice as fast, it will slow down and wait, causing your framerate to drop and giving invalid benchmarks results (lower than what your computer is capable of).
So benchmarks with V-Sync on are a bad idea.
With G-Sync/VRR, the GPU renders frames as fast as it can, and sends them to the display. The display draws them as soon as it can; instantly if enough time has passed since the last frame; there is no scheduled window.
If the GPU can render faster than the monitor can draw, your settings decide what happens, at least for NVIDIA cards. Either it caps at the screen’s max refresh rate as with V-Sync (bad for benchmarks), or you get tearing and a higher framerate (good for benchmarks).
So in short, I would expect that if you have it uncapped once reaching the monitor’s refresh rate, the results should be the same as having no sync and not limiting your benchmarks.
I don’t see the point of having the monitor off, though. Not only is it unlikely to matter, but it’s not a realistic scenario. Why not benchmark the way you will actually play – with the monitor on?