It doesn't have to be fastest, it just has to be faster than what you're using now. C++ compiler has a suite of automatic compiler optimizations that'll make your code performant. Things like loop unrolling, strength reduction, vectorization, cache optimization can make your code many times faster than what you can muster with js.
There's a reason why many AAA titles use C++. No benchmark necessary.
You should probably identify and quantify the bottlenecks first. My guess is this in an XY problem and you’re IO bound or your architecture is doing something bad like a linear complexity algo calling a linear complexity algo in your iteration, and a 1:1 translation to C++ probably won’t have much benefit.
Maybe Fortran?
C++ should be a good solution https://pvapoint.com/buy-bulk-instagram-accounts/
As for the choice of language, it's going to be heavily motivated by what languages you (or your team) know how to benchmark and optimize. It doesn't matter if, say, Befunge is the "fastest" if you don't have anybody working on it that can optimize it.