I was out last night on local roads, and could do a 40mph check,
6th gear, 40 MPH, approx. 1450RPM, so 80 would be 2900 (and you could peg the speedometer at 180 at 5800 if downhill...) I have a OBD2 dongle, and a GPS, could get actual numbers tonight, I don't think our tach is very accurate on the low end.
I will test 60 on the gauges today.
Also, I have the factory tires on the rear.