I dont know what the best ratio is, but I use 6.88. I never rev higher than 6000 RPM

We run 733 in one car and 738 in the other. We tried the 688 that Brad runs but with the cam/engine in the 18 car it KILLED the car getting off the corner. I think it's more a function of getting your final drive ratio to work with your cam profile.

As for the 6000 rpm figure you mentioned I think it's more a function of the engine's ability to breathe rather than gear ratio that governs this figure. At one point we were allowed an edelbrock 2701 intake and the car would turn 6500 rpm, now with stock manifold only 6000 as you stated.

Be cautious with your final gear...too much will give sustained high rpm which is very hard on valve train components both springs and rocker arms, even studs.

Good Luck, Dan McCown