On the fsb thing.
P4, Xeon and Itanium 2 have no where near as much memory bandwidth as AMD64(FX) or Opterons. The AMD64 cpus work at an effective fsb of their mhz. Giving the Opteron cpus up to 1.8ghz FSBs at the moment .

Toms hardware did a comparism a while ago and a Dual Opteron 240 could outperform a Xeon 3.2ghz in nearly every single test (only a few tests that were optimised for Intel cpus did it fail), and even then in some cases it performed higher than the Xeon in the intel optimised tests.

And remember these are 32 bit tests and don't nearly show the power of a 64 bit cpu.