To be up front, it is very difficult to compare the senior jerseys with the pro-style jerseys as they have a very different fit.
The size 50 pro-style jersey measures 25" across the chest (when you lay the jersey flat on a table and measure just under the arms). When we last attempted to measure the senior jerseys, we found that the size XL measured about 24.5" across the chest. The size XXL senior jersey is 26.5" across the chest.
Please keep in mind that the sleeves are also very different in terms of room and length. The pro-style jerseys have much more room in the sleeves to make room for your elbow pads. The pro-style sweater's sleeves are about 2" longer than the senior jersey.