В том то и дело что я после прочтения всего этого и задумался...
Смутило вот что (http://www.freebsd.org/releases/5.5R/hardware-amd64.html):

As of this writing, the following processors are supported:

AMD Athlon64 (``Clawhammer'').

AMD Opteron (``Sledgehammer'').

Intel 64-bit Xeon (``Nacona''). This processor is fabricated on 90nm process technology, and operates with 2.80 to 3.60 GHz (FSB 800MHz) and Intel E7520/E7525/E7320 chipsets.
                                                                      
Intel Pentium 4 Processor supporting Intel EM64T (``Prescott''). This is fabricated on 90nm process technology, uses FC-LGA775 package, and operates with 3.20F/3.40F/3.60F GHz and Intel 925X Express chipsets. The corresponding S-Spec numbers are SL7L9, SL7L8, SL7LA, SL7NZ, SL7PZ, and SL7PX. Note that processors marked as 5xx numbers do not support EM64T.