Per language comparisons vary, but one undiscussed reason why C++ often has the most win is because it allows you to control memory layout for data structures.

Per language comparisons vary, but one undiscussed reason why C++ often has the most win is because it allows you to control memory layout for data structures. The ability to store objects in data structures as values (instead of with references to separately-allocated objects), pack structures to certain sizes, and align to cache are as important as optimizations from the compiler.