Performance drop between 200 and 133 you mean? I don't think you would be able to tell the difference if everything else stayed at the same speed. In benchmarks you would be able to tell though.
If you are on a 2.4B now, and are thinking of switching to a 2.4C I probably wouldn't do it since you are already at 3.1ghz and you probably wouldn't gain that much performance. However almost all processors are now 200 FSB, when coupled with HT, then overclocked you would see a performance increase that is not only in benchmarks.