Overclocking your sound card would produce no benefit, as Svol said. It could even cause it to work badly, if the FSB was raised beyond what the card could handle.
However, if you had a PCI bus hogging card like the SBLive, and a gigabit network card, then the gigabit would most likely be bottlenecked by the bus. Raising the PCI bus speed would very likely remove that bottleneck.
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