From the 1st Barrera fight to present is the best of Pacquiao & in that time only Morales & Marquez have bettered him (Morales more clearly) Its hard to say what was his PEAK performance was tho, there are a few that could be argued.... Diaz-Mosely is his most dominant spell tho since stepping up in class (MAB 1)
From marquez 2 (the night I felt the wild brawler was replaced by a supreme boxer) to present. Spin **** however we want but the guys has dominated, at welterweight, oscar, cotto, clottey, margo and mosle. 3 of them were top 5 at the time of the fight. Aside from ortiz he's cleaned house in dominant fashion.
The 4-fight streak from David Diaz through Oscar De La Hoya and Ricky Hatton to Miguel Cotto. In some fights Manny looked awesome before this streak (Morales II), and in some fights after that streak Manny looked awesome (Margarito), but I still think there was something a little extra and a little special in that particular 12-18 month period.
I think the Margo fight took a lot of steam out of him. Just look at his face and his words in the post fight interview.