Velocity of ringularity
$$
    K_\text{min}=2\pi\sqrt{a^2+3(ma^2)^{2/3}}
\tag{1}
$$
where the quantities $m$ and $a$, both of which have units of length, are defined by
$$
    m=\frac{GM}{c^2}
\hskip2cm
    a=\frac{J}{Mc}.
\tag{2}
$$
The maximum spin is a=m (an extremal Kerr black hole), the borderline case between a black hole and a naked singularity.
More details from Chiral Anomaly here:
https://physics.stackexchange.com/a/469282/