Depends.
In the Anime, SSR is just Goku Black’s normal SSJ. So presumably, it’s just like, 50x. This fits the scaling more too, when you consider Black tanked punches in Base and then went SSR, where he fought SSB Goku and Vegeta and had distinct advantage despite ultimately being their superior. An 8 million times jump just fits less there than a 50x one.
In the Manga, Black has both SSJ and SSR, where even though he has natural God Ki, he still has to consciously combine the energies as it’s a matter of biology and spirit being mixed, not solely one or the other. So he gets a SSB buff, which is directly supported by the fact Zamasu considers the form HIS SSB. Presumably, then, even having natural God Ki wouldn’t alter your form unless you consciously allowed it to do so.