Hmm if you have the system packed with expansion cards, that bumps up the temperature too. Having an intake fan on the left side panel (like <A HREF="http://www.3dcool.com/" target="_new">3DCool's</A> Tornado Cases) helps a great deal in those situations.
Oh, and the temperature difference seems to be about normal--my case has a 7-degree temp difference (23 degrees case, 40 degrees CPU). You need to get your case temperature down though.
bash-2.04$ kill -9 1
init: Just what do you think you're doing, Dave?