Is this voltage good enough?

Well, depends what you call stable, it's good for an i7 chip, C0 especially.

It passed Intel Burn Test 2.3 10 times on maximum. So..well..I guess it is stable,
and one more question on my another PC
Which is using Athlon II 250, i'm looking for low idle power and i saw this

http://www.anandtech.com/show/2836/9

and showed that Athlon II 630 has a lower idle power than my 250.
How can this happen that a quad having lower idle than a dual?

Probably either a glitchy reading, or Athlon II X4s shut down unused cores/have better energy management.