I run the whh dual rudder spdIII setup on my gtx. I use it as a sport boat in calm and rough water. My thought is that two rudders is twice the control. The rudders are in clean water, like an offset, and are in the water through turns in both directions. I'm satisfied with how my boat runs. Also, two rudders doesn't necessarily mean twice the drag. The two rudders can be shorter than a single, since the boat banks into the turn dropping the inside rudder deeper. My 20 lb 65" single Zen boat tops at almost 40 mph. With a big block, I'm shooting for 50 mph.