Rear End Help
 

I have a 1970 Mach 1 and i have installed a 460. i hvae a ford/SVO racing cam which has around .006" of lift. I was thinking about putting 3.89 gears in it with a 3000-3500 stall. However with that combo i won't have a good long distance speed considering i'll be ruunning close to 4500 RPM at 70 MPH. What i want is to hvae great low to mid range power, because i can use my nitrous for my high end. What gear and stall speed should i install to have good long distance races?