How can you benchmark it? The benefit of multithreading is the ability to do more than one thing at a time is it not? Like the ability to update a progress bar in a dialog whilst in the middle of a while loop? Like the ability to be able to carry on using mIRC whilst it is in the middle of a huge $findfile() command?
The benefits of multi threading are so plainly obvious that I'm not sure benchmarks are actually necessary.
