If you do a long Prime run and you are using your computer at the same time for other things, it is possible for the amount of work that each thread does to get a little out of sync but this is much more than normal.

RealTemp 2.70 does not handle hyper threading correctly on Core i7 so it shows the temperatures for the first 4 threads which belong to core 0 and core 1. It does not show the temperature for all 4 cores. The PROCHOT# flag within the CPU has been set for the first two threads which belong to core 0 so the screen shot shows that this core was throttling or reaching 100C, likely during the test. When this happens, the multiplier cycles down to 12. You can't tell from the screen shot whether this CPU throttled once or twice or was throttling continuously for hours but it definitely did some throttling. With early versions of RealTemp there was no way to reset the thermal throttling flag unless you knew how to edit some registers within the CPU or re-booted. Restarting RealTemp would not clear the flag that is set within the CPU. You should be able to clear this flag with newer versions of RealTemp by clicking on the Reset button. I can't remember what version I added that feature.

RealTemp reports 4195.23 MHz. It didn't know about turbo mode back then so it was using a 20X multiplier. 4195.23 / 20 = 209.76 BCLK which agrees with CPU-Z. If throttling was continuous then it would be only 209.76 x 12 = 2517 MHz. With turbo enabled and functioning, it would be 209.76 x 21 = 4404.96 MHz which agrees with CPU-Z. Hopefully some new screen shots at full load will clear this all up.