I have a set of Shimano Ultegra pedals like yours. They are my third try and they are every bit more comfortable than any other pedal I have ever owned. I think your problem lies with the fit of your shoes. You of course should try repositioning your cleats. I wouldn't try any other brand of pedal. Look and Shimano road pedals of your type are the best you can find. The platform is broad and should not cause any stress on any given portion of the foot. Do your road shoes have very stiff soles? If not that is part of your problem.