Ive had alot of "jags" over the years so this is just my personally experience.
Ive grown them up with RD, texas, dempseys, blackbelts and similiar big CA cichlids. They hold there own most of the time. I would say there almost as aggressive as RD/midas, more aggressive than dempseys but different jags will have different temperments. I had a 6" salvini that nearly killed a 7.5" jag but then Ive had a 8" jag kill a 10" texas.
I think its all about territory, introducing a 10" jag to a tank with a established 8" RD will probably end up with a badly beaten jag but if you switch it around (established jag) youll end up with a beat up RD.
Raising them from juvi in a large tank would be your best bet, letting them have there own turf to defend.
So yes they can defend them selves quite well given the right enviroment. But theres always a risk when housing large CA cichlids, when they start to mature you really have to keep an eye on them and a spare tank should be on hand in case a fish flips out. Give them alot of room, dont put a jag and a midas in a 90g and exspect them to spend there lives in there.