Indiscernable/negligible.  The difference (if any) is smaller than the noise floor of benchmarks.

In this particular case, I actually felt a little dirty using `PyDict_Copy`, because it wasn't obviously justified from benchmarks.  It wasn't common for me to use the C API if it wasn't justified with a performance gain (I actually can't think of any other place where I did).  I think my initial benchmarks made it look like `PyDict_Copy` *may* be faster, but I didn't perform enough benchmarks to verify this, and I have not been able to reproduce the result.