The internal clock is the same whether it's 1x100 or 100x1, the greater bus speed could go to waste, but you'll never have less performance from a processor with the same clock that has a higher FSB.
Let me explain a bit more in case that doesn't make sense.
The reason that a multiplier was originally started was because there were instructions that took more than one clock cycle to complete. So they started using a multiplier so that it would finish faster, but they wouldn't have to raise the FSB (and deal with those hassles). So a 2.4GHz processor with a 100MHz bus has the exact same IPC (disregarding RAM or other system factors) as a 2.4GHz processor with a 155MHz bus. The difference is that the bandwidth between it and the RAM is greater unless you bump the RAM back down to the original FSB. However, even if the RAM is bumped back down, the processor is still a higher clockspeed, so you get the same benefit as if you had a higher multiplier.
So (in theory), when you have two processors with the same clockspeed, the one with the higher multiplier would <b>never</b> give better performance. It might give the same performance, but never better.
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