cpu temp should be the temp of the 'package' cores should be the temps of the cores, so they should be loosely related, but not an average. 70+ seems very high, and does not seem right with the cores being 30C, can you use realtemp and do a sensor test, i'm concerned that the cores aren't measuring temps properly.
Your temps are fine, SpeedFan is wrong on newer gen Intel CPU's on certain boards (mine included). It incorrectly detects the VRM sensor as the CPU sensor, for whatever reason. I really wish people would stop using it because I have to tell someone that daily.
Use HWMonitor and look at "Package" temp. That's the REAL CPU temp (besides the cores, of course).