The "rough surface theory" really only applies where the fuel is already in the air as in carb cars. Ours have no fuel until inside the cylinders. I'll go with smooth. Large gauge wire such as 0-gauge "bottlenecks" through relatively small inline fuses but you don't just make the whole current path small. Less restriction means more power. No reason not to improve airflow through the manifolds just because of restriction at the heads. I just installed the Needswings manifolds this weekend and I can tell you there is a substantial increase in power.