We talk about the fifth gear ratio but never talk about the torque range of the motor nor tire size, and rear end ratio that all play into the equation.
Does your motor have the torque at 2,000 rpms (which I consider to be a good cruising range) to cruise down the hiway smoothly, without trailer hitch jerking?
You can change tire size or rear end ratio to help.
I can count 11 different Cobras in our group that can cruise at 1,900 - 2,200 range with easy.
Big blocks and small block with carbs, that I had driven or rode with. Rears end are 3.31, 3.54, 3.55, 3.25. Tires, this I'm not as sure about but I would say 26" - 27" tires.
All have .64 fifth gear.
I have been around several that cruise at 2,800 - 3,000 rpms though the years but they were guys not in our immediate group. I kept wishing they would shift before the motor came apart
but they loved the sound. Each to his own.
You can pick your parts. Build your car. If you don't like something then spend the time and money to change it till you like it.
That's why some things I did four or five times. Part of the fun.
Some guys build pyramids, some build cars. I like cars
Dwight