I love Grados for metal and hard rock. Guitar sounds absolutely amazing. But they are considered bass light by many people. Ultrasone HFI-580s are great for bass heavy music, but they can't touch the Grados for metal and other types of rock. Also, in case you are looking to use these outside your home, the Ultrasones are very portable with pretty good isolation. The Grados are open; everyone can hear your music, and you can hear people talking--not good at all for portable use.
I would suggest go with the Grados since metal seems to be your main love. You won't regret it. Then get some Ultrasones later on for listening to bass heavy music. I have a pair of each--Ultrasones for EDM, and Grados for hard rock--exactly for that reason
If you go with the Grados, order the L-Cush pads that are used on the higher model Grados. They will improve the detail and the bass response (although not to the point that someone would call them a bass heavy phone). Definitely worth the extra $20.