AMD Athlon 64 Overclocking
X-bit labs - Articles - AMD Athlon 64 3400 CPU Review Overclocking. A good piece about the latest AMD processor. The net is that the design of the current chip (Newcastle) limits the actual clock frequency to less than 2.4GHz. The folks at Xbit think that this is due to the design of the chip. In this benchmark, they got the thing to 2.37GHz (215MHz FSB from 200MHz FSB).
This means that even with the ACP/PCI buses locked on the 754 pin Newcastle chips, you'll maybe get to 2.4GHz before you run into trouble.