As the above poster said, the WSKO is variable speed. It can be run quite slowly, which is nice. Middle to upper middle speed (6 through 9 or so) are a great speed for not taking off too much at once, yet getting some work done.
It comes with several more grits of belts than the standard WS. I believe there are quite a few more types and grits of belts available for the WSKO as well. I have about 8 different grits and types for mine.
The WSKO comes with a fully adjustable angle guide, as opposed to the two angle, fixed guide, that comes with the standard WS. I do not use my angle guide; just mentioning it because it's part of the package.
The WSKO has a locking trigger so you can run it without holding the trigger down. Not sure if the standard WS does or not. I've used my WSKO quite a lot and recommend it.
Brian.