You really need to go top-down for what the Cs will sign any player for, and for how long. And the premise I think is this: the Cs want to have large amounts of cap room in 2012 preferably enough to even sign 2 max contract guys. That summer Chris Paul, Deron Williams, and Dwight Howard can all opt out. Carmelo Anthony could be unrestricted if he exercises his option in 2011. And, of course, if Durant wanted to play out the string to get out of OKC, and just go for the qualifying offer in 2011-12, he could be an unrestricted free agent in 2012. Now not all those players will likely be available but some will, and other very good players will likely be free agents.
So KG and Rasheed are up in the summer of 2012, and there is no way RA gets more than 2 years on an extension next summer, so even if resigned he'll be up in 2012. I sincerely doubt the Cs sign any free agent next summer for longer than 2 years, and likely no big contracts in 2011. Although some S&T for a big name is possible in 2011 if for example OKC thinks they'll lose Durant anyway in 2011 or 2012 and takes Rondo, Perk, draft picks, etc. in exchange.
So the 3 major names who could be on the team pasr 2012 are Rondo, Perk, and Pierce.
Rondo will be a difficult call because if the Cs see him as a top-5 point guard, they may just need to pay him whatever the market will yield, but I suspect they'll even hold the line there to what they think is his value, or perhaps go a little beyond. Pierce is going to be a very interesting because if he exercises his option next summer and is unrestricted in 2011, how much do pay a guy (and for how long) who is in the pantheon of Celtics greats, but will be 34 at the start of the 2011 season? The Cs I imagine would like him to bridge to the new generation, and hel draw some free agents in 2012, but going more than 3 years seems unwise and would Pierce take $10M per at this stage of his career? Would he demand to be up more like $15M?
After the Rondo and Pierce contract situations are clarified, and you get a pulse on what free agency in 2012 is going to looks like, then you decide what to do with Perk. If Rondo and Pierce are making reasonable money, or if one left, you may be able to overpay Perk slightly (I put his value around $7M/year so that's where the judgment starts, and I would never pay him $10M+) because he is a good solid defensive NBA center and a known quantity, and if the free agents you are going to target supplement a core of Rondo, Perk, and for 1 to 2 years an old Pierce, this may make sense. However, if Rondo and Pierce got top dollar you may decide Perk can not be signed even at a decent market value because that would prevent the signing of a star player in 2012. And if Dwight Howard is your 2012 target and you feel good about your chances, then you make due with whoever at center in 2011-12 and wave goodbye to Perk.