Something harder than Muse but easier than Iron Maiden. Something around the difficulty of Cliff-era Metallica besides Cliff-era Metallica.
you could look into Caught in a Mosh by Anthrax. Not really that hard, it's just fast.
Take something beyond your ability and slow it down to half speed. Slowly speed up as you're comfortable.
Some Coheed is around there. Mostly stuff from SSTB and IKSSE: 3. And IMO, aside from Hysteria, Muse stuff seems pretty easy.