The freezing of motion has more to do with the duration of the light than it does with the speed of a shutter. Obviously, with a continuous source of light, the only way to reduce the duration of it is with your shutter, but when you do control the light, that's a very different story.

The technique I use to freeze the motion of something like water requires a very dark room, a long(ish) shutter speed, and a very brief flash (usually off camera). My typical setup, for water drops, is:

1. Dark room, basement works well for this.
2. 1 second shutter speed at lowest ISO (100 usually, though my K-5 goes as low as 80).
3. Flash set to 1/64th or 1/32nd power pointed at a background.
4. Radio triggers with a test button.
5. Cable release for the camera.

What I'll do then is trip the shutter and then manually fire the flash. It'll take a few tries, but generally I can get a very high success rate with the approach. An example of an end result can be seen on my Flickr stream and I have a lot more details on my site.

As a note, I think HSS is actually making it worse for you. The use of HSS causes light pulses and, since the duration is what matters, you will have a bunch of durations recording on your image. That isn't going to help.