Thats a little high as below 50 C IMHO is better. Voltage isnt the problem as far as the heat issue, but a good psu would deliver 12.5v,5.06v,and 3.4v.
Here are some quick and easy things to do to improve the temps:
1. Install a better HSF than the one that came in the box. ie.. vantek(cant remember), dragon orb3, sk6, wbk38 etc. (anything with a copper core or all copper with a good fan)<A HREF="http://www.dansdata.com/coolercomp.htm" target="_new">Goto 52 cooler comparison here</A>
2. Use artic silverII thermal paste on the cpu core, its way better.
3. Add a front case fan to blow some fresh air into the case.
4. Add a rear extraction fan up top to remove that hot air.(recommended)
Another thing I have just installed is the Digidoc5 monitoring unit found at <A HREF="http://www.macpower.com.tw/digitaldoc5.htm" target="_new">macpower</A>. For overclockers this thing is a heavenly gift.
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