In my best Riggleism it depends. Not sure what the 55MPH revs are on my vehicles but I can give you 75 MPH.

69 Mustang 351W 120 MPH 6400 RPM oops that is a bit more than 75.

01 BMW M5 5.0 V8 75 MPH just a touch over 2500 RPM.

03 Excursion 6.8 V10 75 MPH ... Login to read more.