metal and rock are my main genres, and i own the atticus and did own an eikon (so you already know my personal preference!). i find both excellent for metal, you wont be disappointed either way. the eikon has more upper mid/low treble extension, so guitars are louder and more forward vs the atticus. i'm sensitive in that frequency range so i preferred the atticus. both have tremendous bass slam, the difference is the atticus is a bit thicker sounding due to it's mid bass hump. most metal doesnt go very low so the eikon's slightly stronger sub bass extension is mostly moot. bass on them is more similar than different though, so either way, you're getting some really nice bass. the single biggest difference to me was that upper mid/low treble extension on the eikon. if you want a lighter, more linear sound, the eikon is probably better. if you want something a bit thicker and warmer, the atticus reigns supreme. in the end your best bet is get to a local meet or store if possible to try them out, one will resonate with you more than the other. on paper i thought i'd end up with an eikon. but after listening, the atticus was my personal favorite.
another thing, both are kinda picky on amps. you can get nice sound out of something as simple as a magni, but they really respond to certain amps. they're much like the hd600/650 in that regard. they can go from ho hum to breathtaking with a simple amp change. my personal favorite amps for the atticus are both violectric/lake people. the rs-08 and v280 both balanced. the v100 and rs-02 are no slouch either on the single ended side. the molnir 2 was quite nice as well. on the eikon side, i really liked my buddies woo wa3 since it softened the treble a bit. funny thing though, i didnt like the atticus on it at all. and i didnt like the eikon much on the rs-08 or v100, but did like it on the v280. like i said, picky azz headphones when it comes to amp synergy! but once you get the right setup, wow...