Yes, I am talking about CPU core temperature difference between Everest and RealTemp.

I have similar high NB temperature at ~60C under benchmarking. However I set my NB voltage at 1.53V. The NB voltage setting depends on the PL level you select. Mine is PL10 with FSB=496MHz. I found this configuration to be quite stable (though I tried PL9 at one time and it is fine too).

An excellent NB voltage vs. performance article can be found at http://www.anandtech.com/showdoc.aspx?i=3208&p=5