The prominence of the room mic is entirely dependent on the context. With most speedy metal mixes, a prominent room mic is just going to clutter up your drums, especially the kick drum. When I use room mics for metal, it's usually pretty low, just to even out the overheads / spot cymbal mics. You might have better luck triggering a room mic sample on just the snare if you're after the "bigness". That way, you won't have to deal with the kick getting all cluttered up.