Unless you absolutely want a CS-1 4". I would keep the National Match 5". Way harder to come by than a 4" CS gun. And 5" guns are way cool.
In my experience shooting a few of the CS 4" guns, guys had for the service revolver match. They shot no better than most 4" L frames. They were popular because it was easy to change the front sight to a Patridge type sight.
You know the funny thing. When Davis had those made, guys couldn't figure, why a 5". Open class PPC allowed a 6", Distinguished revolver match 6". Service revolver match 4". Unless it was allowed in some bullseye event. But like someone said maybe some were awarded as prizes. Or Bill wanted something different!