AMD's work differently. They don't rely on clock speed like Pentium 4's.
That Opteron 146 has the same San Diego core as the FX-57, and they can overclock insanely high even on stock voltage.
Hell, that Opteron 146 could kick your Pentium 4's ass twice. Don't just think that because you can get a higher clock means that your processor is faster. It isn't.
The older ones usually have fans on the heatsink. Now that the 5200 is essentially outdated, they use cheaper methods of cooling, and that results in the use of just a big aluminum heatsink.
GG alinvo and correct aswell opteron would "kick teh shizzer" into that p4 with like you said same core, overlcockerbility, and that Cache...yes please!