I wouldn't put Dats with them. I had a Gar in my 125 and they get way too big for a 125. I would put a couple of small convicts. I know this sounds white trash, but they are scrappy and cool little fish. They would also give your other fish plenty of room. If you had a male and female they will team up against the other fish, so they aren't pushed around too much either.
I'm getting a 125g next month and I was wondering what I could stock this with, I already have to put my Jaguar cichlid and Flowerhorn in it and I was wondering if there was any other catfish,Characin, or pretty much any other predator I could put in here.