It's worth noting that "gilding metal" can be composed of different ratios of copper and zinc. I don't know for sure but I would surmise that Hornady's gilding metal is softer (uses less zinc) than Nosler's.
The reason I believe this is because when seating a bullet into a case with a compressed load, the Nosler bullets will seat confidently with no excessive marring on the jacket from the seating die.
Hornady bullets on the other hand tend to have 'softer' seats and the impression from the seating die is more like a scuff or scrape across the surface of the jacket. I can show a picture if you'd like.
That's why I believe that Hornady uses less zinc in their Gilding metal which would bring the GMX closer in its ability to open at lower velocities like Barnes bullets. I would suggest that perhaps the E-tip would require higher velocities to open well although I've never shot an animal with an E-tip.
All I can say for sure is that the GMX seems to be quite capable based on my experience. If it can open well in the small neck of a white tail deer which is itself a small animal, it will surely open well in a moose or elk. I didn't recover the bullet, obviously, but I can infer that expansion is good from the wound channel.