I think there is a misconception here that if Pierce opt out he will be taking a discount.
1) Pierce picks up his option and gets an extension.
$21 + $10 + $11 + $12 = $54 Million over 4 years
2) Pierce opts out and signs a new deal
$14 + $14 + $14 + $14 = $56 Million over 4 years
If he chooses "2" he will be making a smart business decision for himself and help the Celtics avoid luxury tax penalties... Not taking a discount.
Edit - I fixed it.
First off, I don't see PP walking away from a $21 mill payday next year. Financially foolish on his part. Secondly, I'd be against offering him your proposed second option. His salary drop isn't going to make the team a factor in the free agent market to make it worth it. Also, I'd rather he take less $ in the extension with a declining amount each year to correspond to the anticipated decline in his game.
He stands to make about $2 mill per year more than Ray will get in his extension. I'd offer Pierce 11, 10, 9 for the 3 years after that (10, 9, 8 would be better). Do the same for Ray. Hope KG signs for another year extension at about 10/11 for the year.
Even with those contracts for PP/Ray/KG, figure Perk and Rondo for 10 per year at that point and you're looking at $50 mill for your starters. With luck, Danny has stocked the bench with affordable, quality players through the draft and prudent MLE signings so that Wyc isn't taking a beating with the luxury tax.
In any event, the C's won't be a player in free agency until at least 2 of the big 3 retire (or move on) and even then, they'll need to really restock via the draft or trades