The buff is explained in this question: How does the Nephalem Valor buff work?. It is said that there are
hidden effects, and I'd like to know those.
From diablo.incgamers.com (Nephalem Valor > Magic Find... MF is Broken)
I used 140MF without NV buff and went to kill Zoltan Kull and he drop non of yellow in 10 games. When I have 0 MF and stack of Nephalem Valor (5) 75% mf I'm getting 1-3 yellow and 3-5 blues.
I experience the same effect: if I do siegebreaker runs with magic find gear switch, I am up to 130% mf, and I still have poorer loot that when I kill him with 5 stacks at 75% mf. So what are the hidden effects of the NV buff ?