IMO Galaxea is one of the most aggressive coral I've ever had. As already stated, I've seen their nematocysts reach as far as 8" from the body and sting anything within its reach. If the Galaxea is in a corner of a tank, they will only need about 8". However, if the coral is placed in the center of a tank, then it'll need 8" in all directions.....and THAT takes up a ton of room.
In contrast I've seen my Torch reach almost as far as the Galaxea but don't seem to be nearly as aggressive or toxic as the Galaxea.
This is all from my observations.
Russ