strange temps - need help with offset?

Sorry about yet another temp question but I searched the posts and didn't see anything related (and yes I have read the temp guide - many times).

Just completed a build using a Gigabyte 965P-DS3, E6320, Zalman 9500 hsf. no overclocking yet but using manual settings in bios. Plenty of airflow (4 case fans + p/s).

Ambiant = 22C
CPU temp at idle is reading 35C, Cores at 28C/30C
CPU temp at load (TAT 100%) is 53C, Cores at 45C/44C as reported

Temperatures relatively consistent between Speedfan, TAT, bios (cpu), and Everest.

Why is the cpu temp always higher than the core temps?

If an offset is needed, which one do I raise or lower and by how much? As an example, the temperature guide indicates a 15C difference between cpu and core - do I raise the core offsets by 22C (35 cpu + 15 = 50, 50 - reported 28C on core = 22C)?? OR do I lower the cpu offset (but this seems too low)??

Also, this is my first build using Vista - could this be software related?

Any / all guidance is welcome - Thanks!