narrower than 23mm
I use Competition on all my bikes and I gave a try GP4000, the first feeling is the width because it is so narrow. Less cushion than Competition and bad grip when wet also on gravel, may be it's the shape of the tire being more triangle at the center than equal round. Now it's just an expensive spare tire under my saddle (it's light).
May be that is why most pros use Competition instead of GP4000.