I think what we should be looking at is that the performance can asymptotically approach C, where C is used because it's the closest to the theoretical optimum assembly that is still practical for writing large programs.
If a language can get arbitrarily close to C in performance, it starts to become a much better design trade-off to use.
One of the touted benefits of pure strongly typed code in languages like Haskell or OCaml is that they can compile to assembler that is faster than C, because the compiler can guarantee certain behaviors and thereby increase sharing of computations and insert multicore parallelism .
I think what we should be looking at is that the performance can asymptotically approach C, where C is used because it's the closest to the theoretical optimum assembly that is still practical for writing large programs.
If a language can get arbitrarily close to C in performance, it starts to become a much better design trade-off to use.