If Bargnani comes out and averages 9 boards per game for the first 20 games, I will be
amazed. If he maintains his 1:4 OR

R historical ratio, that means he would average 7.2 DR a game, or a 24% DRR based upon 35-36 mpg.
In my opinion, that's a very, very high bar to set to just be pleasently surprised.
I would be very happy if he (defensive) rebounded at an average rate for a big (19-20%) and continue rebounding at his historical OR:OR ratio. This would translate into 7.0 to 7.4 total rebounds per game.