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+1 @ Jeff on all points. Additionally, I might look at haircut for the first one, cropping just under the blue sky.
As a general aspect of motion blur, the slower the shutter the more the motion blur. But it is also distance/magnification related, so your relative distance to the motion (and orientation) and focal length can be components as well ... i.e. closer = more blur (comp/framing notwithstanding).
ND filters (or polarizing filters) can reduce the amount of light as well, to warrant a slower shutter speed. The choice at how much blur is always a subjective one from flowing milky white to frozen droplets, so only you can answer the question @ "Do I want to slow the shutter?"
A couple of tools that you may have not thought about are your watch and a compass (metaphoric or literal). Orientation to the sky, relative to the sun's position throughout the time of day can impact your lighting from specular to soft, as well as the amount of light.
Classicly, overcast days are often cited as good days for waterfalls, for the even lighting and lower illumination levels. But if you pay attention to the orientation of the fall vs. the open sky @ time of day, you can get a somewhat reduced illumination level there too (just have to adjust for WB @ time of day/orientation) that will allow for slower shutters.