I don't listen to metal, so I can't comment on how well Spartacus fares vs other IEMs.
But one thing I do know about metal is that speed and precision are key to reproduce drum & guitar details properly, and in my listening to Tidal's "The Metallist" playlist, Spartacus' 4xBAs are keeping up exceptionally well:
https://tidal.com/browse/playlist/7c50bdc8-a448-452c-9289-20815c6140e9
Add the glow & warmth from the BCDs, you get a nice large stage for all of the instruments to breathe well, with no congestion or wonkiness.
Again, I don't know these tracks to know if I'm missing anything with Spartacus, but the more I'm listening, the more I'm really enjoying this.