: The Daizenshuu are passed through and noted by Akira Toriyama and made with both his scrutiny and Approval. That means they're canon and they are the Most Canon Source outside the Source Material itself, the Original Manga. Brolly doesn't exist in the Manga universe so you can't claim the Daizenshuu has nothing to do with him when Vol6 was made Explicitly to encompass the DBZ movies. So, no matter how much you whine about it, it doesn't change the fact that the Daizenshuu made specific explanations concerning the movies, and they told us Goku and Gohan were SS2. That makes their word infinitely more legit than your ramblings.
And you want estimates on speed? In truth Toriyama had stated that the 1mil/km mark on Snake Way was just a random number because he couldn't really think of the astronomical unit involved and because he wanted to keep the series Simple to Understand. But what we actually see when comparing the position of the Check-In station and Snake Way with King Kai's planet when overlapping the actual Physical Universe itself, shows an extreme distance crossing easily millions of lightyears.
Dragon Ball Universe
Now, even if we took the 1mil/km at face value, Goku still crossed it with a speed of mach 28 in Flight. As noted in earlier parts, their Reaction Speed is far greater than their Travel Speed. Which is indicated by Piccolo (and Roshi's) moon-busting attack which struck the Moon in just shy if 4sec. Given the shortest distance between the Surface of the Earth and the Moon is roughly 320thousand kilometers, that made it around 1/4th the speed of light. And this was before Nappa and Vegeta arrived on Earth.
But let's see for travel. Goku at 8000pl could Fly at Mach 28. Kaioken and SSJ forms provide direct multiplication to all physical stats from this point forward. Goku by Buu Saga had a base level of 60mil. That's 7500 times greater. So 7500 x 28 = Mach 210,000. Goku's Base Speed in Flight is now just shy of one-quarter lightspeed, making his Reaction Time far greater. Then we multiply this by the Super Saiyan 2 increase, which is 100fold. 210k becomes 21mil, making Goku's SS2 Travel speed just under 24x Lightspeed. Gohan's at SS2 is not much different and Brolly still smacked him around like nobodies business.
And to just drive home the point of Power differences.
in English Dub and Japanese Dub, the result is still the same, and performed by Brolly, who was under the Control Circlet, which Diminishes his power and Restrains him from using his maximum strength at all times, preventing him from going beyond a Psuedo-SSJ form. Meaning Brolly wasn't even in his Legendary status when he all but annihilated the Southern Galaxy.