I was totally with you until the part about Metallica. Fade to Black and Sanitarium are the very definitions of what solos should be. Kirk Hammett is a master.
While Fade to Black and Sanitarium have great solos, for balls ass metal solos I would have to say that Frayed Ends of Sanity, Dyers Eve, and Struggle Within are at the very top.
And though he rarely solos, and his solos are nothing special, and the thread is about solos, without question, the undisputed king of down picking is James Hetfield.