how much difference between 3.91 and 4.10

pettybludart said
My Dart Sport Has 4.10 Gear 255 60. 15. 65mph=3000rpm.so I Would Think 3.91 Would Be Somewhere Around 2700.hope This Helps.

My 69 dart 3.91 is at 3600 rpm at 65 with a 245/60/15 i must have a looser converter 2800