Yes, it is safe, as long as it is a stable OC. The thing is, at start up, it won't be using the OC anyways, assuming you assigned it to the 3D profile. It will only OC when you enter a 3D game.
I would, however, warn you about such a large memory OC. You get limited benefits from the memory OC, and DDR5 tends to be far more likely to wear out rapidly with too high of an OC, even if it seems stable.
Ah ok, what do you suggest I make the memory OC to then?