Originally Posted by Schmuckley
Inbefore XD...Yes you should underclock and undervolt it..2.4 should be OK..just undervolt as much as you can but keep it stable.You could go a little lower on the clocks,too
I'm honestly not sure if it'll even be an issue, considering its an old school K8 duallie.
Honestly, you're even lucky enough to have gotten 3.4GHz out of a K8. Those 6400+ chips were pretty well already at their max clock speeds out of the box.
My HTPC02 build has a 125w Athlon 64 x2 6000+ installed.....on a cheap OEM Gateway motherboard (which I'm sure is "technically" 65w or 95w rated). And its been going solid for YEARS.