Pentium 4s are too hot.
And when it comes to performance, even the Athlon 64 3200 can beat the Pentium 3.4GHz EE (5/10 the time in 32-Bit, 1/0 the time in 64-Bit)
Tom is wrong and corrupt.
PCWorld is a better friend.
And for RAM:
Athlon 64 - Up to PC3200 w/ or w/o Registered DDR
Athlon 64 FX - Up to PC3200 w/ Registered DDR (Requires Registered DDR. Registered DDR doesn't have to be ECC.)
Opteron 148, 248, 848 - Same as Athlon 64 FX
Opteron Below 148, 248, 8458 - Same as Athlon 64 FX except maximum RAM is not PC3200 but PC2700