Intel Celeron 430
This post covers a successful upgrade
My Supermicro rtr had a Pentium 4 2.8 w/ TH for the longest time but it ran so hot. \
Today I down graded (or upgraded?) to the 430 and Wow! This thing runs cool. If anyone is looking for a cool proc with good performance then the 430 is for you. Best proc I think you can find for socket 775.
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116039 And its $40 w/ free shipping.
Although I currently don't have a pfSense system set up, I can safely say that you are right since I had a Celeron 430 running FreeNAS (based on m0n0wall) and I had no problems either. Ran nice and cool, and the CPU utilisation never rose above 2%, all for £30!
The only reason why I wanted to post about the up/downGrade was because it runs so cool.
My Server is a 1U system, so the CPU cooler was really loud to keep that hot proc cooled. I am now throttling the CPU cooler at 4000 RPM and the Proc won't go a single degree over 48C!
I'm loving it and if someone is building a system then the 430 is for you. 1.8 Ghz single core is enough trust me.