Chapter: 469 (DBZ 275), P5.6-7
Goku: “Damn it! If either Vegeta or Gohan were alive, maybe we could have managed something…”
Piccolo: “…No, it probably wouldn’t matter how many people went at him…He wasn’t at that level…”
Implied that even if SSJ2 Goku, Vegeta, and Gohan teamed up they still wouldn't beat Fat Boo
Chapter: 479 (DBZ 285), P5.2-4
Context: when the Z Sword breaks, after Gohan trained with it for a day
Gohan: “But…thanks to that, my arm strength has increased a lot. That Z Sword was incredibly heavy, after all…Perhaps this was what they meant by me obtaining the greatest power in the world.”
Kaioshin: “I-I get it…If he’s acquired that much power in his regular state, then if he becomes a Super Saiyan it will become an even more substantial power-up…! Ye-yeah! That’s it! That’s definitely the greatest power in the world…!”
Goku: “…But…Is he greater than Majin Boo?...I wonder…”
Gohan Is said to rival Fat Boo in power. Kaioshin states just SSJ but I assume he doesn't really realize the difference between them so I assume SSJ2.
Gohan far outclasses Goku and Vegeta.