The star rotating at 500 RPS is the little one, the one whose mass is 1% of the sun and has six times the density of lead. I doubt that something with twice the mass of the sun could rotate that fast even if it was at neutron star density. The tangential velocity of the perimeter would likely be a significant fraction of the speed of light (thats a guess).
Still, the little guy is pretty damned impressive.
500 rps is about 10% of the speed of light (assume 10 km radius of the neutron star).
I believe its the Neutron star, the larger of the two, that is rotating at 30,000 RPM. The diameter is estimated at about 20km. Someone do the math!
https://phys.org/news/2020-10-mystery-unusual-neutron-star-revealed.html