For me the answer (speed) is not as given as for you guys. Because I have been playing with simulations of hulls. And from what I could learn, these light hulls have a pretty negligible wave resistance. So the width is not as important as in heavier boats. The wetted surface is the important parameter. But on a second look, it looks like the hull is already stretching the beam a bit away from the ideal. So I think this explains it. If it is made wider, it will have higher wetted surface. When the dimension are close to the ideal beam, large changes in beam results in only small changes in surface area. But if the beam is already stretched, an increase might results in a noticeable increase in area / decrease in speed. So it's a matter of how far from ideal it is now, if it can be stretched without a penalty.