Your processor has energy saving feature so when its not doing anything @ idle it reduces the voltage and speed to 1600 and 0.768v Its normal.
C1E is power saving (Speedstep) handled directly by the CPU itself.
EIST is the same as C1E, except it's handled by the operating system instead of the CPU.
If you enable C1E and set windows 7 to max performance, it will still downclock to 1600 mhz, because the cpu/motherboard is handling the power saving.
If you enable EIST and set windows to max performance, it will act the same as if EIST was disabled (not downclock).
If you donot want this then disable the energy saving features of the CPU from bios.
Normaly its not recommended but wont do any damage either.