1. Well for me Reign in Blood is the king of early thrash albums with Exodus`s Bonded by Blood a close second and early Metallica and Megadeth as well. When it comes to thrash and groove metal Slayer, Sepultura and Pantera are really it for me, even though I do have a very soft spot for Megadeth.
2. Without doubt Cliff Burton was one of the best bass players of his generation and I don`t think that Metallica ever replaced him, I was never a fan really of John Newstead.
3. Well you know far more about both ACDC and Motorhead than I do, so I`ll bow to your better judgement there, as my knowledge is based on just several albums between them. As for Orgasmatron, well I love Sepultura`s version of the song.