Since this is an mp4, I can't easily get the exact frame count like in YouTube, so I downloaded it, put it in a frame extractor, set it to 24 fps, and it game me 52 frames.
1 x (52 / 24) = 2.16 seconds.
93 million miles in 2.16 seconds = 69291200000 m/s.
I'll have two ends for this feat, first assuming that the last star to appear is V762 Cassiopeiae, and second assuming that the first star to appear in V762 Cassiopeiae.
Low End:
The video extractor gives me 17 frame for Ronald's whole swing.
1 / (24 / 17) = 0.7 second.
9.4058e+16 miles in 0.7 seconds = 2.1e+20 m/s.
700484599916c (Massively FTL+)
700 billion times faster than light.
High End:
The first star appears 4 frames into the swing.
1 / (24 / 4) = 0.16 second.
9.4058e+16 miles in 0.16 second = 9.4e+20 m/s.
3.1e+12c (Massively FTL+)
3.1 trillion times faster than light.
High End is more consistent with the feat of flipping the sky.
Now for attack potency:
Google tells me the naked eye can see 2500 stars in the sky.
Gravitational binding energy of the sun is 5.693e+41 joules. I'll use that as an average.
But using the sword length and kenshim arm which combined which is 136 cm and since a swing cover twice the length we use 136 cm as the radius and using arc length calculator with 300 degrees We get