[kragen]

You don't need the whole Python interpreter to fall back to dynamic method dispatch for overloaded operators. CPython itself implements them with per-interface vtables for C extensions, very similar to Golang but laboriously constructed by hand.

For most code, you don't need static typing for most overloaded operators to get decent performance, either. From my experience with Ur-Scheme, even a simple prediction that most arithmetic is on (small) integers with a runtime typecheck and conditional jump before inlining the integer version of each arithmetic operation performs remarkably well—not competitive with C but several times faster than CPython. It costs you an extra conditional branch in the case where the type is something else, but you need that check anyway if you are going to have unboxed integers, and it's smallish compared to the call and return you'll need once you find the correct overload to call. (I didn't implement overloading in Ur-Scheme, just exiting with an error message.)

Even concatenating strings is slow enough that checking the tag bits to see if you are adding integers won't make it much slower.

Where this approach really falls down is choosing between integer and floating point math. (Also, you really don't want to box your floats.)

And of course inline caches and PICs are well-known techniques for handling this kind of thing efficiently. They originated in JIT compilers, but you can use them in AOT compilers too; Ian Piumarta showed that.