Buff Buu vs Mystic Gohan

I'd say Gohan can probably still take him, but it'd be a much more difficult fight.

EDIT: It'd likely be another fight like SSj3 Goku and Gotenks had with their respective evil versions of Boo; practically dead-even with the outcome uncertain. The one advantage Gohan would have, however, is that his power wouldn't be getting flushed away more and more every second like Goku and Gotenks' was thanks to SSj3. If Gohan manages to turn the battle in his favor, he wouldn't have nearly as much trouble building up for a finishing blast.

Based on Goku's reaction when Buff Buu was formed; it's safe to say this his power is on a whole different level compared to the regular Super Buu. But if that's enough to turn the tables on Gohan; possibly, but I'm more inclined to remain on Gohan's side on this one.

i think buff buu is simalar in power to super buu
so ultimate gohan wins

Well if we go by a simple
SSJ3 goku 1
SSj3 gotenks/super buu 1.5
Gohan 2
And then give super buu a powerup from becoming buff buu, it will probably put him around gohans level.
I feel gohan would win this though because he most likely has speed and smarts to his advantage in this fight, and as previously stated he doesn't constantly drain energy

How can he have the same power and be stronger all the same? It's one or the other man...

But for the record; it's the second option.

With the way goku was worried about buff buu, I would say he was significantly stronger then supes. I would have him a tiny bit below chou gohan, so gohan takes this but with a lot harder battle.