Some of the stuff is this thread is pretty ridiculous. A lot of it is plain wrong. Big 4 doesn't always apply to a lot of genres/movements/sub-genres/etc.
Slayer is more popular, has sold more records, and had far more influence than Testament ever did. Just look at last.fm, where Slayer has more than 2.5x as many listeners. Hell, Legacy/Testament didn't even release a demo until 1985, when thrash had already taken off. Testament really isn't any more popular than the teutonic thrashers or Exodus, either (and is certainly far less influential than either), so why would they get in before Kreator, Sodom, or Exodus?
Beyond that, Anthrax would be the first ones kicked out, not Slayer. And that's not just because I don't like Anthrax. They're, by far, the least popular of the big four and were the least influential.
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The Vines, The Hives, The Strokes, and The White Stripes are often sited as the big four "rock saviors/revivalists" of the early 2000s.
...but yes, the psychedelic movement was a huge influence on the symphonic prog scene in the late 60s and early 70s. Some of the other subgenres of prog, not so much, but definitely in symphonic prog.
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Big 4 Of Sludge: Mastodon, Eyehategod, Melvins, High On Fire
But that's just in my opinion. Feel free to correct me.
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