When I ordered my '64 Custom/427, I had a choice of a 4.11 or a 3.50. So I ordered the 4.11. I soon found out that the 4.11 was just fine for running around town, but I needed a 3.50 for highway cruising. I put a set of 8.20X15 tires on the rear, and made a little chart that I taped to the dash. 3000 was about 70 in 4th gear.
The nice thing about the 3.50 was that I could shift back into 3rd at 100 and have a serious passing gear---or just the thing for dealing with 'vettes and 409 chibrolays on the highways. And with the 3.50, 2nd gear was just great for roll-racing around home. Higher-numerical-geared cars were wanting to be in 3rd but I had very usable RPMs left to enable me to get a jump.
I had a top speed of over 150 with the highway combo, but the steering got very light starting at about 130. (The speedo only went to 120, but the needle would show in the 'gen' red light next to the 120 line on the dash.)
KS
KS