[Docs] Update some notes on speed (#19323)

Fixes #19297

Author: kripken

site/source/docs/optimizing/Optimizing-Code.rst

@@ -245,7 +245,7 @@ To ensure that compiled code contains enough information for profiling, build yo
 Troubleshooting poor performance
 ================================
 
-Emscripten-compiled code can currently achieve approximately half the speed of a native build. If the performance is significantly poorer than expected, you can also run through the additional troubleshooting steps below:
+Emscripten-compiled code can often be close to the speed of a native build. If the performance is significantly poorer than expected, you can also run through the additional troubleshooting steps below:
 
 -  :ref:`Building-Projects` is a two-stage process: compiling source code files to LLVM **and** generating JavaScript from LLVM. Did you build using the same optimization values in **both** steps (``-O2`` or ``-O3``)?
 -  Test on multiple browsers. If performance is acceptable on one browser and significantly poorer on another, then :ref:`file a bug report <bug-reports>`, noting the problem browser and other relevant information.