4.7 with 1.2v is a good overclock.
For me I used to get
4.7 at 1.25v
4.8 at 1.3v
4.9 at 1.36v
5 at 1.45v
I regret running it at 1.45v as the electron migration really devastated my CPU. I can no longer run at those speeds with those voltages. For 4.7, I now need 1.32v for the system to be stable. So now im running at 4.4 at 1.2v