Keep in mind that a 1.25" hollow bar will have a rate similar to a 1.125" solid bar. The difference in wall thickness of the hollow bar is why they have to go to larger diameter to maintain rates vs the solid bar. A 1.25" solid bar produces more rate than a 1.25" hollow bar.

If you not concerned about a slight weight penalty or achieving ultimate performance, than go with a simple, and less expensive, 1.125" solid unit that is widely available for reasonable cost.