Goku, under the water when fighting Frieza, said "Kamehameha" in his mind while floating under water. Goku has summoned energy attacks WHILE not saying anything. Things such as the energy blasts while fighting Majin Vegeta. His Kamehameha wave while doing the Instant Transmission. Now, people have said "Goku can instant transmission [x] before Superman Reaches him, or before [x] reaches him." And yes, we HAVE seen what Goku is capable of in the sense that we saw him fighting at his full potential vs. Buu, and then vs. Omega Shenron. We saw him put his full effort into it. We saw him training, and how he trains.
As for the Instant Transmission thing--he uses his Ki whenever he transmits, secondly, he has to have a point of reference; it's not Instantaneous movement, like Dende or some of the Kai's have (less effective), and he hasn't had a clock'd speed. We cannot assume how FAST he is. Just "faster than the naked eye." Which means, what, he's Sonic's speed? Now, you say I need to think deeper? Okay then--Goku broke out of hell (in the DBZ anime, not in the manga) that's a feat only few have ever done. He trained at 100x Earth's gravity and hit himself with a full charge Kamehameha. He's capable of taking strong ki based attacks to the face (in DBGT). Then WHY, and this is important because I didn't want to pull it out, does he still bleed after being punched through a mountain?
We've seen Bizarro Superman (in Superman's body) get punched THROUGH the Earth, out the other side, with no pain and just a smile on his face. We've seen Superman punch someone THROUGH the Earth, and around the Earth. When people mention how strong Goku is--we have seen him punch someone THROUGH a mountain; and if you take the Pikkon Goku fight in the DBZ anime. When Goku uses his Super Kaioken, he catches Pikkon off guard, and punches him into the "moon" like thing above the stadium. After doing so, it creates a massive crater. But it doesn't destroy it. We'lll assume he doesn't NEED to say Kamehameha and go from there. There is still the motion needed to preform the Kamehameha. Which is putting your hands behind your back, and summoning the Ki, and then putting your hands forward.
Ki is still Life Force, though. People say that "The kamehameha moves at light speed" because "We've seen it blow up the moon in a matter of seconds." and we've also seen Cooler hurl'd toward the sun in "0:10 during his fight." But that doesn't mean that's how fast it is. Technically, the Afterimage requires beyond light speed movement, but then why isn't ALL of their movement an afterimage? It's not JUST a technique, if you're going to use physics one should do it properly.
Now, let's just assume (since that's the name of the game when using Goku), he can have his arms straight forward, and his Kamehameha charges INSTANTLY (instead of taking seconds to charge, of which--that could be used to screw up his day),) that he does fire that beam. He is totally helpless if that beam goes flying into nothingness. Goku is weak during that entire time until he can cease the beam. Next. the idea that Goku can destroy a planet is entirely fathomable. Just because we have to go by the assumption DBZ Chars know what they're talking about:
"Goku, don't use the Spirit bomb, you can destroy the planet." Or even during the fight with Cell "Goku, if you fire directly at the ground you'll destroy the planet." I think it is completely understandable to believe Goku capable of destroying a planet. But not breaking through dimensions. Gotenks did it? Okay--let's talk a bit about Gotenks. Gotenks flew around the world 8 times, napped, and then came back. And was almost immediately brought out of Fusion when Piccolo found him. So that means within 30 minutes he did this. Superman flew to another Galaxy while hearing people call out in pain; he saved them, and then came back--and Lois didn't even realize he had left.
That kind of topples "flying around the world in 8 seconds." Also--Goku got to Earth before Piccolo died in the Saiyan saga. Appeared right before his son had gotten smashed--and saved him. Goku was out of the regenerative pod on Namek, and flew halfway around the planet, but it took him longer to get there than it should have. Goku is NOT that fast, he moves beyond the speed of sound, at least. But there's no way he moves faster than the speed of light (at least, not when flying, maybe when punching?). But again, we cannot ASSUME this. There are lots of assumptions that people have to make when using DBZ because there is NO real physics to it (lolphysics).. Gotenks can break through the Hyperbolic Time Chamber, into reality, like Buu? Okay--Superman punched through another dimension, he's punched THROUGH a barrier used by the Green Lantern, and escaped a double black hole.
Goku hasn't done that so we cannot ASSUME he can do that. I can't think of a movie, or an episode where Goku did that. Essentially, that would be the barrier Frieza used against him on Namek, if he could escape that prior to it exploding, then yes. But he didn't. He escaped it during the explosion and so he IS faster than that. He was hardly scathed but that's it.
- TRUST ME. I Agree with you that Goku would lose, and be crush'd hard compared to Superman. The only reason I say "assume" is because people will say things like "we don't know what Goku's capable of" but the only reason I use "assumptions" is because lots of DBZ Fanboys can't fathom the loss of their favorite hero. Even though Goku's my favorite hero, I know he'd lose. And the only reason I keep "assuming" things is just because even UNDER such circumstances, Goku's still not at an advantage. So--sorry if it seems I'm a Gokufanboy, but I'm not. But I have to use assumptions to make the DBZboys happy, when they see the loss of their Superhero.