I wish manufacturers and users would have standardized technical terms to describe parts and features.
The core speed (CPU GHz) is obtained by the Bus Speed (adjustable) multiplied by the "Multiplier" which in most cases if fixed (Non-adjustable Multiplier)
In my case, I have an Intel i7-920 CPU with a fixed multiplier of 21 - I have raised the Bus Speed to 182. This gives me 182x21 = 3.82GHz CPU speed.
Then there is the RAM multiplier, sometimes referred to as RAM ratio. This multiplier must be set at the LOWEST setting (maybe 8) before doing any overclocking. The reason for this is because the RAM frequency also increases as the CPU speed is increased, and you do not want to exceed the RAM manufacturer's rated speed. Underclocking the RAM by a small amount is perfectly acceptable. In fact, my 1600 MHz RAM is underclocked to 1452 MHz.
Hope this helps.