This'd be the form he used back in the Buu saga after the Elder Supreme Kai helped him (I like calling it 'Mystic Gohan'). It's around SSJ3 level but without the endurance problems.
Gohan has always been more gifted than Goku when it came to power, he just lack the motivation to train. After the Cell saga he stop training like Goku to reach a new ssj form. But when he did train, he was always shown to be able reach a new level of power faster than Goku. He should be more power than Goku even at ssj4 level because he has more hidden power than Goku does. Goku has always been shown to have to work a little harder to reach a new level (ssj2). So Gohan's mystic powers should put him above ssj4 Goku, if we ignore the fact that Gohan was able to go ssj in GT.
Did I misremember? Well, at the very least, Gohan was doing *much* better against Superbuu than SSJ3 Gotenks did, and SSJ3 Gotenks was much stronger than SSJ3 Goku.
While he was a good deal more powerful than DBZ SSJ3 Goku, I don't think it means he is at the same level as that of DBGT SSJ4 Goku, who made his SSJ3 form look piss-poor in comparison, and iirc, DBGT Goku was more powerful than his DBZ version.
And yeah, Super Buu with Gotenks powering him was trouncing Gohan, though I believe Gohan held his own for a brief time. Which is why Goku wanted to fuse with Gohan in the first place.
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"To all visitors from Transylvania looking for the head of Voivode Dracula: Yes, we have it. Yes, he's dead. No, you cannot see it. No, he will not return and invade you again. It has been over thirty years, please stop pestering us."
It doesn't, but when you take into account that Goku stated Super Baby Vegeta was stronger than anyone else he had encountered (which includes Super Buu w/ Gohan absorbed), SSJ4 Goku would have to be far more powerful than the Gohan that fought Super Buu.
The kid thing didn't expressly weaken him in terms of power level I think, and between DBZ & DBGT, Goku had been training. Heck, in GT, Goku takes out both Cell & Freeza in his base form.
__________________
"To all visitors from Transylvania looking for the head of Voivode Dracula: Yes, we have it. Yes, he's dead. No, you cannot see it. No, he will not return and invade you again. It has been over thirty years, please stop pestering us."
Ok. It sounds to me like Gohan's power might be a similar multiplier to SSJ4... but Goku's base was much higher by that point so he's still easily the stronger anyway.
Possibly. I can't accurately tell. SSJ4 is still the superior amp though.
Of course. I did not even bother to mention him.
__________________
"To all visitors from Transylvania looking for the head of Voivode Dracula: Yes, we have it. Yes, he's dead. No, you cannot see it. No, he will not return and invade you again. It has been over thirty years, please stop pestering us."
Gohan reached his max potential, meaning that he couldn't get stronger. The reason why he couldn't power up to a super saiyan was because of this reason.
Gohan's potential was hinted to be beyond that of Goku through the entire series, meaning that Gohan should have become more powerful than Goku could ever become.
Going by the power level chart super saiyan three Goku has a power level of 2.4⋿10 and super Buu a power level of 3.6⋿10, or 1.5 times that of Goku's. Gohan in turn was strictly more powerful than super Buu.
The most reasonable estimate of Gohan's power level would be twice that of Goku's.