I dont know all the flow# but I always told rect ports will loose bottom end torque and they like really high rpms to get the most out of them. How big of a big block ?
Oval ports are better over all head for most applications. What is this motor you are putting these on. Single plane intake or dual plane ? A while back I had a 56 chevy, 427,team g single plane,950hp holley and rect ports. It ran good but I would of have changed to oval ports for the street/toy if I kept it.