When I bought my 68 400 it had a 4:11 gear set in it. The previous owner had it set up (very poorly in my opinion) as a drag car. The 4:11 was useless on the highway. Awesome acceleration but a top speed of maybe 55 mph and constant overheat problems. I changed to 3:73 which was better but still pretty crappy on the highway. Last fall I changed again to 3:55 which was another step up. I still have the great acceleration but now I have an ok cruiser on the highway. I can cruise at 70-75 for as far as I want to go (no more than an hour or two to semi-local meets and shows). In hind sight I probably should have gone with something taller like the 3:08. You definitely dont need low gearing in the rearend with a pontiac motor. They produce tons of torque and lots of low-end power so anything more than 3:55 is likely to give you something you dont really want. Oh I run a 400 4-speed with a 12-bolt posi.