Could you link that calc?
Sure. I posted it earlier but I'll repost here.
Also honestly Roshis feat at 13 sec which is accurate for anime timeframe is 0.0986 times the speed of light, so less than 1.4% faster and he hits it, so he should probably just be relativistic since he is virtually there already and he had juice left in the tank after the attack, and anybody superior would logically be relativistic even if you didn't give him the 1.4%. And I mean the moon can be as much as 405,696 km away from the Earth depending on time of year, so you cold even argue the feat might already be in relativistic level since those above numbers are from its average distance.
Although if we want to be more accurate with Roshi's moon buster and use speed of dispersion it would be higher. Kep actually did that out using 20 seconds as a timeframe for me a while back for dispersion as an estimate for the manga. It comes out as 5-B
vsbattles.fandom.com
In the show they notice Goku is gone after reverting when the moon is gone, thus the moon would logically have been dispersed before the time they notice this. From the point we see the attack hit and begin to explode on the moon in a omnidirectional blast till they notice Goku is "gone" and Krillin runs toward the ring yelling his name 40 seconds lapses from 1:44-2:24
If we replace Keps velocity with one that disperses over 40 seconds we get 0.5*7.34767309e+22*130,275^2 = 6.23508E+32 J Or 5-B still using anime timeframe.
So if we go with Keps suggestion on a manga timeframe, or use the anime timeframe, we actually get 5-B, which is consistent for DBZ Piccolos anime timeframe of 4 Sec which will result in 5-A based on previous calcs.
Now some people still may argue for using vaporization, but that really doesn't work since if the matter were not dispersed you would still see all the gas created from vaporization where the moon was still, but there is nothing there in anime and manga, and to disperse the gas you'd still need to move the same mass at that speed. Also we know in DB virtually every celestial body that is destroyed by a ki blast has been depicted as a violent omnidirectional explosion, from Frieza blowing up Planet Vegeta and Namek, to Buu destroying earth in both anime and manga. So it would be inconsistent if Roshi's attack only vaporized the moon and didn't apply for using kinetic energy tbh.
So if we want to iron out the speed and most accurate calculation for his feat, I vote for using the speed above from the anime since we can get an actual timeframe that way, and the timeframe for the moons dispersal from the anime, or Keps suggestion of 20 sec as a estimate for a more accurate AP.
So 5-B Max power Roshi with relativistic speed honestly is where I think he realistically stands after ironing out the speed and kinetic energy calc.