If you don't need to read the vbo on the cpu side and if you don't have to update many different parts of the vbo it would propably be faster to just push updates to the vbo using GL.BufferSubData. That way the driver doesn't have to retrieve the data back from the gpu. This is because mapping the buffer has the driver retrieve the specified part of vbo from vram into ram and then on unmap transfering the whole thing back to vram. With buffersubdata it never retrieves anything from gpu and only updates the part specified in the command.
But all of the methods suggested here are valid and the only way of knowing wich one has the most performance is to profile them with your actual use case. And when doing that you propably should look into highprecision timer and timing individual frames. Keep a list of say 600 frames and you can get the shortest the longest and the avarage. Measuring performance in how many milliseconds or if you want even in nanoseconds is important as that gives a much better idea of just how much your performance drops than frames per second. Also keeping a record of individual frames lets you see the longest frames and help you find stutters and such more easily.
All you have to worry about is if your frame time exceeds 16 milliseconds then you can no longer quarantee 60 fps and you might need to optimize. Or if you are targeting a differrent fps(for vr i think you need over 90 and for mobile 30 should be enough) you can calculate the millisecond limit by 1000/fps.