The speed of your servers may be limited by quite a few things. Some likely things are connections with users and connections with databases. If you want to improve speed, find the bottleneck and fix it. If your CPU usage is 30% while your internet connections are swamped, improving the speed of your programs will do almost nothing. Similarly, if your back end processing is dominated by database operations, speeding the code up will do very little.
If you're doing a lot of computation per hit, then it is possible that application speed itself is important, and if you can do the computation in a language designed for it like C++ or Fortran you might speed things up enough to be worthwhile. Here I'm recommending doing the computation in a normally fast language, not the whole thing. A language like Python handling the requests and passing off the hard stuff to C++ modules will usually do very nicely.
Normally, before doing that, I'd like to do a stress test on the system to see if it actually matters. Run one server until it maxes out, and see where it's maxed out or nearly maxed out. Fix that if possible, and you may want to try it again. Don't worry about specific types of performance until you have good reason to believe it matters.