unless you are hauling a lot of weight or want the lower rear ratio for pulling power, I would stay with the 6.17 gears. The 2-speed is 6.40 and 8.75. That is nice for pulling a lot of weight because you have more gears but, it has a slower top end. My 1958 6400 spins about 3500-4000 going down the freeway. (depending on how fast I push it), 34-3500 I am getting passed by everyone, 3600-3700 I am keeping up with traffic. if I want to get in front of a slower moving vehicle, I am pushing the 4000 mark.
