I don't have much experience with any of the speakers you mentioned, so my advice should be taken with a grain of salt. I've heard them, but not for any length of time to give the insight the others here have...
If you're really intrigued by Harbeths, you should definitely make it a point to hear them. When I was speaker shopping, I heard a bunch of speakers. There were some excellent ones that I'd easily have been happy with. Something told me to track down Audio Physic. I'd almost made my mind up when I went to a dealer on the way back from another audition. Unbeknownst to me, he carried the speaker I was looking for. It was exactly what I was looking for in a speaker, and then some. I've happily had them for 4 years, and they blow the doors off everything I've heard anywhere near their price.
I'm not saying buy Audio Physics. I'm saying if you're truly interested in the Harbeths, find a way to hear them. Harbeths don't have a cult following for nothing. They're excellent speakers that I think everyone in this hobby should hear at least once.
ProAcs are excellent speakers as well. Keep in mind the best speaker will most likely be the one that fits your room and system best. If you have a bigger room, the Studio 100 may end up sounding better than the 1SC, even though the 1SC is a "better" speaker, lineup wise.