As far as Moissanite being more brittle than CZ, this statement has been made before, and it simply isn't true and the science doesn't support this claim.
I can't agree with this from a practical standpoint however. In our experience, moissanite rounds are much more vulnerable to chipping than CZ rounds.
While it may be true when comparing a block of material to a block of material (which is how the various tests measuring these things are done), customers aren't wearing cubes of material, but rather cut stones.
Anyway, during the time we used to sell moissanite, in our experience round moissanite is much more prone to chipping via the girdle edge than round CZ. We saw this when setting moissanite vs. setting Asha, as well as when customers were sending in moissanite rings to be replaced....there was a fair amount of chipped rounds.
I suspect that Charles and Colvard was, at least then, cutting their girdles really thin in order to minimize color tinting, but at the same time, it makes the edges much more vulnerable.
This effect is also true in diamond - i.e. once a stone is cut, if the edge is quite thin, the actual strength of the material will not likely be enough to protect it fully.
This is why, material aside, princess cuts (with their thin edges) are much more prone to chipping than a round, which has a thicker edge by comparison.
Thus, eliminating the strength of material and simply comparing cuts (diamond round vs. diamond princess) you can see the practical effect of having a thinner edge on the worn stone and its resultant increase in risk of chipping.
The takeaway is that simply showing that a cube of material is stronger than another cube of material does not have as much as a practical bearing on risk of chipping vs. how thin an exposed edge is.
I also noted for some time that Moissanite (at least previously) did not warranty against chipping and the above is likely why.
That said, Mikes point is correct regarding mounting choices - the more 'airy' and light the setting is for rings, the more it leaves the stone (any stone) vulnerable to potential damage.