It is a useful skill but a little early and only as one skill not the only skill. One topic a year would be OK if it were used in a variety of ways for a range of skills (Rome could be used to jump into geography, transport, logistics etc). Gifted kids on the whole seem more sensitive so gore and inhumanity are even less appropriate. It seems like a lot of NT kids can say 'it was a long time ago' whereas gifted kids think a bit more deeply and put it together with other information.