x86 clock speed importance?

[superfury]

How important is it for an x86 to run at a certain speed compared to hardware? So running at 4.77Mhz when operating VGA registers or other hardware, how important is it for the processor to be in sync, from the programmers (emulator) perspective? Will it cause problems with written software if the processor is too fast, compared to used hardware? How does the PIT chip factor in all of this?