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DrFish,
At FPS limit ON, it uses the hardware timer to control the FPS thus the CPU is able to Sleep when waiting for the Timer interrupt.
When the SS is running at FPS limit OFF, it is not using the hardware timer but actually has a max limit of 250 fps so Sleep is called directly to keep it max at 250 fps thus CPU is able to rest.
Note that MA2-MD using DirectX 6 sourcebase which may not take advantage of new advances in DirectX.
When VSync On, DirectX is in control of the CPU when waiting for the Vertical Blank. My guess here based on some tests is that DirectX is actually looping the CPU while waiting for the vertical blank, thus uses more CPU at FPS limit OFF.
I am beginning to agree with Morgan about raising the MaxSpeed for FPS Limit higher than 60 fps so people with higher Monitor rates can take advantage of less CPU usage and VSync on.
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