One thing I had a look at is that konan does not allow specifying code generation. Using SIMD instruction sets available on modern processors makes a big difference for calculation heavy tasks, but compilers are normally conservative in the code they generate (to avoid using unavailable instructions). For this reason it is possible in gcc and clang to specify the hardware level (what instructions are allowed) as well as tuning (what processor to optimize for). I assume that this will be added at some point.
In the meantime you can compile to LLVM bitcode and use llc to compile it to an executable.