With the (very) warm M-Stage, I'd rather go for the HE-4 for metal.
Even on my SA-31 (which is less warm than the M-Stage) I feel the 5LEs are a bit soft with hard-rock/metal. They make wonder with classic rock, blues, vocal (the 500s are king here, IMO) and instrumental.
Think of the HE-4 as a more refined K-702 with much more bass impact (note: the bass is boosted in the lowest bass region for added impact but no bass bump like on the 500s) a fuller and warmer sound and no harshness.
It just fall short of the 702s in sound-stage but not many headphones can match them in that department
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I would need to listen to the 702s or 601s (own) again because when I switched from the 701s (sold) to the 4s, I noticed the latter had much better depth and layering than the AKG, yet more intimate (especially with the M-Stage which reaches its limit with the 4s but I listen at moderate volume. That was with the old velour pads though).