With my set up, in 4th gear, the speed in miles per hour is just about double the rpms in hundreds; so at 3,000 rpm (30 hundred) the speed is 60 mph; at 2,000 rpm, it's 40 mph. This also tells me that if I go to the red line, it will be slightly over 120 mph (if the car holds together.)
My numbers are: 3.92 rear end, 205/70X14 rear tires.
Richard M