Over the years that I have used WSM I have been constantly amazed at the sheer number and usefulness of the revisions. Ton Brand leaves others in the dust when it comes to constant development and tech support.
There are other competitors out there but, for sheer speed, performance, features and value for money, this application should be at the top of your list of "Must Have" list if you want a fast loading website.
The author has a very interesting comparison chart which can be viewed at ....
http://www.tonbrand.nl/wsmmactest.htm