I would just call him back and say, Sorry I can't afford that in such a short amount of time, BUT I can pay $xx by xx/xx but ONLY if you change the rating to an R5. That's what *I* would do. You don't owe a large amount, so if it DOES go unpaid for a little longer I dont see them coming after you for it. Once you call him also send a letter saying the same, that way IF they DO bring you to court, you can show you made an effort to settle this matter quickly, without wasting the courts time.
I wouldn't necessarily let on (I mean, they probably know people share information about this stuff) that you know others have settled for less. I would just convey that you really, really want to take care of this asap, but the amount is a little steep due to paying it in full--ask if there is anything they can do to reduce ut and still get the R5 rating. I am assuming that he have you the complete and correct balance. Just negotiate, but don't let on that you have an idea as to how the system works, if that makes sense. And in all honesty, my husband got farther with Mr. Cooke's dept so far as combining 2 accounts and getting a good interest rate, so I think they try to do all they can. But sometimes you have to ask a little, if that makes sense! Give 'em a nudge as to what you want. Good luck and congrats on getting this fixed!!!!