70c isn't big for an overclocked unit. And 1.3v is sweet. Other users have needed 1.4v to get 4.1ghz on their ryzen 2600.
But like everyone said, are you sacrificing 15c for 3 more FPS?
You gotta find the sweet spot. The lowest voltage that gets you the most noticeable boost.
Example : 3.9ghz at 1.13v
4ghz at 1.15v
4.1ghz at 1.23v
4.1ghz at 1.3
Of course, in this case, you stay to 4ghz. Gotta check the numbers on tutorials cos I put mine randomly.