Best feats of GT:
Base Goku was stronger than Base Rildo whose power was much greater than Majin Buu:
Starting with Kid Goku, his power was so great in Base form that not even Rildo could calculate his powers. even for futuristic computers, who can likely calculate more digits then our computers which can what calculate millions and trillions of digits. So it would be far above the trillions, quitillions, ect, But for Rildo it was IMPOSSIBLE!
In the fight against Base Baby, He was sent to another dimension by Base Baby Death ball, his power was so great that it warped Goku into another dimension:
He was sent to a dimension when you can't use Ki or else you will be stuck in that dimension for ever. The host cheats and the space is collapsing. Goku decided to use his Ki to blow up the dimension:
Later after Baby transformed twice he use the same technic, but this time much much powerful that the one that warped space and send Goku into another dimension.
Yet Goku in SSJ4 tanked all the power of the revenge ball without a scratch:
The Evil Dragon was said to have destroyed the cosmos surrounding when he appeared on a planet along time ago.
However this was translated into galaxies, apparently cosmos = galaxies, which is true.
popo: "ずっとずっと昔 ➡邪悪龍 他の星に現れた｡ その星 たちまち滅ぼされ➡その周りの銀河 全部 滅びたという｡" A long long time ago, the Evil Dragon appeared on another planet. That planet was immediately destroyed, as were the galaxies surrounding it
source: dbgt episode 48
Omega stated several times he would destroy the entire universe. The Universe of Dragonball is bigger than our universe, since it contains several dimensions and the After life.:
俺は 破滅の戦士だ｡➡この体にみなぎる ﾏｲﾅｽﾊﾟﾜｰで お前たちを葬り 地球を破壊し➡そして 全銀河を滅亡させてやる｡ I'm perfect. By obtaining the four star ball I have become perfect. From this moment on, I am god. I'll destroy anything and everything. The god of destruction. I'll utterly destroy the entire universe with my minus power.
surce: dbgt episde 62
Feats that backed up this is the simulation shown by Ro Kaioshin:
Elder Kaioshin/Ro kaioshin. They will not be spared either, fun fact, their dimension is located outside the Macroverse.
This universe/after life corrosion would happen pretty quickly since even Kibitoshin was scared and wanted to rum away, yet he fails to know that there is no where to hide and the fact that he wants to means Omega would quickly wiped the macroverse. Since as you know Kibitoshin was in a dimension outside the macroverse:
Here is the map of the Dragonball universe :
Gogeta stopped the maximum power of Minus energy of Omega casually kicking an universe/after life buster attack.:
Gogeta SSJ4's power was stated limitless and that he was the strongest warrior of all, in GT perfect files:
"Un poder sin límite! La fusión y la prueba de su amistad!"
" A power without limits! The fusion and proof of their friendship"
"The transformation in Super Saiyan 4 Gogeta consumes a quantity of energy that only last 10 minutes!The most powerful warrior of all!"
It was also stated he could end Omega Shenron with a finger if he wanted, the BBK that Omega survived was only PIS, so Goku would beat him with the Universal Spirit Bomb, which by the wasn't as powerful as Gogeta, is also stated that there is no equal to SSJ4 Gogeta. And said to be dozens of times the power of Goku SSJ4.
"A warrior with no equal, born from the fusion of Goku and Vegeta! He has red hair and a character a bit childish. He can defeat Omega Shenlong only with one finger. His strength is dozens of times more powerful than a normal Super Saiyan 4. He can shoot an extraordinary shot, which is a mix of the Big Bang attack and the Kamehameha wave!"
Futur Goku should be astronomically stronger than Gogeta SSJ4,even in base form, since it was implied he became a sort of God and had 100 years of training. He absorbed the Dragonballs and brought back from the dead Puk(Goku's Jr friend):
Note: Gogeta SSJ4 can use BBK x 100 in video games and most likely could have used it against Omega, but didn't because it wasn't unnecessary, since he was pounding him already without trying.
Conclusion GT is Overpowerd it has super galaxy cluster busters, Universe busters to Macroverse busters and potentially a Multiverse buster (Future Goku).One thing I forgot to mention, although Gogeta SSJ4 is extremely powerful, he is still below Beerus and Even SSG Goku, since he doesn't have God Ki, and only Gods can beat Gods, God powers was stated by Goku to belong to another world/realm.