They have, in a number of ways, been our two best bigs this series, but you can't abandon Perk & KG.
As much as I love Davis' hustle and what he's providing on the offensive end, he's a liability on defense. Of the 4 bigs we have (I don't count Sheldon), he's our 3rd best at guarding Bynum and our worst at guarding Gasol. In the first quarter, when KG got in foul trouble, Davis came in and Gasol royally lit him up. He just doesn't have the length to guard Gasol. He doesn't have the length to guard Bynum either (evident by that ally-oop where Bynum practically stood still and caught the ball next to the hoop), but at least he can body him.
I'm not sure what Rasheed's back status is, but he's been our best defender on either Gasol or Bynum (when he's not getting called for ticky-tac fouls). I'd also like to see the Celtics work the ball into the post. He could provide some needed post play and potentially get some of their bigs in foul trouble.