CPU Temp is ~14c hotter than Core temps--Which should I watch?

I have a Asus M5a97 LE R2.0 and an FX-4130. I plan on doing some moderate overclocking once I get heatsinks and an 80mm fan to cool my mosfets. Preliminary tests seem very promising. On my stock cooler (which AMD claims is better than the other stock coolers they offer, the looks and tests of it second that claim) @ 4200mhz, while actually undervolting and stable (P95 for 30+ minutes) I can safely stay below 55c CPU temp. My core temp under full load is actually around 42c so my question is, should I be watching CPU temp or Core temps? From what I read core temp is generally 10c hotter than cpu temp, but for my build its the other way around. I'm a little confused and some google researching just gave me a whole bunch of different answers. I do have excellent case cooling if anyone needed to know that. I've been using both HWmonitor and Core Temp to monitor my temps.

TLDR: CPU temp is much hotter than core temp. Which should I be concerned about when I start overclocking?