ViaHardware has posted an article about how to get to those "hard to reach places", namely 140-150MHz on a P3V4X. Here a clip:

Foremost among the P3V4X´s many "eccentricities" is the seemingly inexplicable instability of a few FSB speeds. 140-150MHz, in particular, seem to be especially hard to get running correctly on this board.

The easiest way to bring stability to your P3V4X at 150MHz is to cool the Clock Generator, and we show you how.

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