That data set is a bit small.
The best fit I've found so far(let U=uscf rating and C=chess.com rating) is
C=-7.3*10-8(U)^4+.000481(U)^3-1.1649(U)^2+1232.21(U)-478642
Yeah, it's nasty, not easy to write in a text editor, and R^2=.7966 so it's probably the best bet I'm going to find without getting out some serious computing power.
However after 1900 or so live chess ratings the competition is very thin and so I think that those ratings will be a bit inaccurate.
Phelon (online) 1949 (live) 1712 (USCF) 1655
Zug (online) 2534 (live) 1837 (USCF) 2208
etc. It seems in general if you see a player with an accurate USCF rating (if he played 4 games 10 years ago it may not be exactly right ;p) it will coincide very well with his most accurate live chess rating, (again if he has only played 2-3 live chess games this rating will be very inaccurate) however his online CC chess rating will be very inflated.