Actually, the Enermax EG451P-V, 450 watt power supply is only AMD Approved up to 1Ghz. From what I understand, this is because the Enermax PSU cannot supply a very good +5 voltage. This is not the same model Newegg is selling. That particular model isn't even listed on AMD's list of approved PSUs. While it may work just fine at 1.4Ghz, there is no guarentee from AMD that it will work at that speed. My friend however has this PSU and its running a 1.2Ghz Athlon just fine.
Here's the link to AMD's recommended Power Supplies:
Link
Also, this is probably not the Whisper version of the PSU. The whisper model is the :
EG465P-VE(FC) model. Newegg's model is the EG465P-VE. Both models are 431watts (Check
Enermax's web site).
The Enermax PSU's are great power supplies, but as of this point, they're not AMD approved for anything above a 1Ghz Athlon, and this particular model hasn't even been tested yet, although I would imagine that they would work just fine up to 1.4Ghz.