This is frankly hearsay and working from memory, but I seem to recall there there was a question mark over reliability of the P4 running at 3.66GHz.
On the face of it, this seems also to be a point made in click here see under "Overclocking".
Another point: We have a couple of P4 3.066GHz machines which we compared with a contact's P4 3.4GHz and, on most practical tasks, there was very little performance uplift, nothing more than +10%.
Obviously the linked report is dated but may assist. HTH.