Overall, they are faster, based upon what I've read(no, not from AMD fanboy sites). Before some Intel fanboy jumps in, let us all be clear that this is about comparing the P4, not the EE.
but then, it could all be BS, but I doubt it. The 64 is a new generation chip and the P4s have been out for a while, so it only makes sense. Also, in the off chance that you use Linux, the AMD64 will slaughter a P4 when using a 64bit kernel. But, that's linux specific, for now...
<i>SCO is to Linux what a flea is to a dog.</i>