If you want pure execution performance, the best scripting language I know is Cling.
It's an interactive C++ interpreter, based on LLVM.
Basically it compiles C++ code interactively within the host application.
That's much more efficient than the DLL compilation hacks (RCCpp, etc)...
And the best part of that is that once your scripts run fine in the C++ interpreter, you can add them to you C++ application build files