After a few years of raising a mix of Treetop and Fork-tailed bush katydids, I've come to notice some distinct physical differences, which I've pointed out in these photos. S. furcata lacks most or all of the black coloration seen in S. fasciata, on both the tegmina and the abdomen and legs. Secondly, S. furcata tends to have a green and yellow/pale white face, whereas S. fasciata has distinct bright white patches which are present early on in growth and persist through adulthood. Lastly, the underside of the abdomen tends to be white, while S. fasciata has some amount of pink or magenta:



The full life cycle of the male is here, and a female I caught as well here.
Hopefully these photographs and information can help distinguish these two species as nymphs and adults a bit easier. Katydids make great pets, they were a delight to raise!