The list of guys who are cut is better to look at since those guys wouldn't count against the comp pick formula..
This is an interesting thought and one I would probably agree with. If we do lose any of Welker, Vollmer or Talib I would hate to miss out on compensation because of lesser free agent signings.
A speculative list of defensive backs that may be cut/cap casualties:
Nnamdi Asomugha
Adrian Wilson
These are the two that would interest me the most if cut. I would have to think Asomugha would be in heaven if he signed with the Pats. After spending most of his career in Oakland and that mess of an organisation, he then signs with Philly who turned out to be as much, if not even more of a train wreck. I would have to think that for a guy that is such a pro, coming to an environment like New England would have to be appealing for him. A well run, professional organisation that gives him a shot to win.
Wilson had a down year, lost playing time as the season went on and is getting up there in years. But he was one of my biggest free agent targets last season and I still think he has something left in the tank. I think he would be a perfect compliment at SS next to McCourty and give us a veteran presence that hopefully a young SS that we draft can learn under. If I remember correctly, in 2011 he was rated as one of the best coverage safeties in the NFL, so I think he could certainly add something to the secondary.
I would have some interest in Freeney , but like others have said it would have to be at the right price and he would need to accept a lesser role. I still think he could add something on 3rd down though. My other top target who I have already talked about is Glenn Dorsey, I think he could be a real sleeper if used in the right way. My ideal FA scenario would be:
Re-sign Welker
Tag and Trade Vollmer (Stl, SD, Chi, Ari, Phi?)
Let Talib walk (and hopefully pick up comp pick)
Sign (if cut)
CB-Asomugha
SS-Wilson
DT- Dorsey (also wouldn't mind taking a shot at Jason Jones, Sammie Lee Hill, Mike DeVito or Terrence Knighton)