Good answer, except for the multithreading part.

Multithreading doesn't improve speed, it improves apparent speed, which is quite different.

Multithreading is actually less efficient. On the surface, doing many things at once like a multithreaded program without using real threads seems more complicated, but real multithreaded programming has so many hidden pitfalls and debugging problems that you would probably have found the increased difficulty of singlethreaded code not that great.

The Accelerating Apache project for example, has managed to make Apache 1.3 up to ten times faster and Apache 2.0 up to four times faster on the SPECweb96 benchmark. A major part of this was ditching threads for their State Thread package, which simulates multithreaded behavior without actually using threads (similar to GNU Pth, by the way).