The changing comparison between British 5.25-inch and American 5-inch guns

How did the British 5.25-inch gun compare with the United States Navy's 5-inch weapon?

The American gun led early in the war, the improved British 5.25-inch may have led around 1944-46, and later American development restored the 5-inch advantage.

The comparison changes with the date because both weapons and their supporting systems evolved. The American 5-inch gun has the advantage around 1942-43. The improved British 5.25-inch becomes more competitive, and possibly superior, around 1944-46. Continued American development then moves the advantage back to the 5-inch system in the postwar period, so the answer depends on the exact service year rather than calibre alone.