Depends... If it's the first CA or a CA working for the OC, they probably won't take anything less than $1600. Anything else will be probably be ignored or sold to another CA. If this is from a JDB (i.e. the 2nd or 3rd CA) then they might be a little more flexible. Given that they validated, I'd guess the former applies more to your case, but that's just me talkin'.
If you're going for a full PFD, then you need to offer payment in full. Remember, you are basically doing a business transaction, and there must be something in it for the CA. Money is a great motivator, and "quick money" is even a stronger one. If they refuse to do a PFD, then start off negotiating a settlement with an offer of 50%, and go from there. A "Paid In Full" versus a "Settled" notation does not really impact your FICO score.