Ernie,
You are very correct. My horsepower is at 5800-6200 RPM and in 5th gear I can't get above 3300 RPM which is 115 MPH because of my gearing and that wall of air. I have 3:27 gears and I chose the wrong split for 5th which kicks the gears up to 2:10 and with this brick I can't even begin to get into my power range. In 4th I can run around 145-150 if I push it. So the rpm, tire size, gears, and about everything including aerdynamics play into what speed you can do at what RPM.
427/SO
You are correct about every conceivable calculator being on a computer. However I like the small ones in the car because we do a lot of comparisons of gears, tire sizes & etc. when we are far away from a computer. My old junker just isn't equiped for the modern options.
Ron