Fluctuating core voltage normal?

Vcore does move around(when it drops its called v-droop. Some boards are better then others.), even more so with speed step on. If its not unstable, do not worry about it.....

In short, yes it moves. and in cases can drop under load(some asus boards have an option to minimize this[voltage dampener or something similar]). If you enable speed step it will go even lower....

you have it set too low thats why it moves so much