A multiplier is the number of times faster the processor is than the bus. You want to use the fastest bus speed supported by your motherboard. In order to do this, you may need to lower the multiplier to relate to the CPU speed. This is controlled by jumper settings on the motherboard, or in SoftMenu if your board is jumperless. Enable the internal cache.
Processors have their own internal cache which operates at the processor's speed.
The newer chips have larger caches. Always have this cache enabled. It helps performance quite a bit. If you can't enable it without problems, it is a sign of a definite hardware problem. Enable External Cache.