I must say, these are ALL valid points. But the biggest tester for a dog in the sheep dept in my humble opinion, regardless of how good it is, and I include my own here for falling short of what is acceptible, is a hill sheep, smaller, more flighty, highly likely to burst out of some fern or cover all on its own, they run different and they smell different, and are much smaller than low gound breeds. I know some will come back with, "a sheep is a sheep", but trust me, it's not. Again this is just my own humble opinion for what its worth.
Regards
B