The light in the spot where you are taking photos will determine what shutter speed etc you need to use. In full shade with just a polarising filter, you can get quite slow shutter speeds, down to a couple of seconds, but if it's sunny you need more light filtering, and you tend to get blown out highlights (like you have in the top 2 photos).
Set ISO to 100 and aperture to as high as you can with the lens you are using eg 22 and start from there with shutter at 1/5 say.
Shutter speed also determines effect. At 1/5 you get good definition of the water movement and as shutter speed gets longer after that you start to get that milky effect. You don't seem to get much more benefit by going to slow with the shutter unless you want the real misty milky effect, and then you need an ND400 filter so you get go the shutter speeds of say 30secs. If you do try an ND400, especially out in the sun, remember to block the viewfinder on your camera
I'm not very good at explaining how to do stuff so I hope this makes sense.