That gap in mph is a lot more than a car or two.
On average stock c6z's trap 124 around here Gen 3's 121 3MPH isn't 6 cars. Now if you want to compare a low side of the scale gen 3 120 MPH trap vs a high side of the scale c6z trap of 127 Then sure 7 MPH is a big gap but, I wouldn't call that the norm.