General :: Does SpeedStep Change Bus Speed Or Just Multiplier?

I want to estimate how a certain piece of code will perform on different Intel Westmere processors. The various processors all support the same QPI and memory speed, and they all have the same cache sizes; the only difference is the CPU core clock speed (2.66GHz vs. 2.93GHz etc.) I already have one such processor running with a very fast CPU core clock. I would like to estimate the performance of the others without having to purchase them first.

Using cpufreq-set on Linux (acpi-cpufreq driver), I can set my core clock speed to a variety of slower values. My question is simply this: Does setting the core clock speed in this way change anything other than the core clock speed? That is, does it precisely simulate a slower CPU, or does it also slow down the front side bus or change the cache size or whatever?