I doubt if the fan speed makes much difference to the noise print.
100% N1 RB211-524D4=3,900rpm, fan diameter=95.00"
JT9D-70A =3,600rpm -:- =95.56"
CF6-50 =3,433rpm
The fan bypass ratio of 5:1 on the RB211 is the highest of all three engines but there is really not much difference in the basics between them except the RB211 of course, which is a three spool engine.