If you really want to squeeze every last nanoflop of performance out of your hardware then you need to turn to languages like C and C++, or if you have a lot of time on your hands, and a large beard, assembler.
There is a reason that these languages are the mainstay of the games development industry.
If you want to generate the fastest Ruby extension possible without having to worry about how you are going to install libraries for HTTP, XML, XPath, SQL, multithreading and file system access (to name a few) then I suggest you check this framework out.
If you want to take on Google and build the greatest number crunching data analysis farm in the world, then its perfect for that too.
Reason is a wonderfully easy to understand cross platform C++ framework. The code is very readable and amazingly well commented.