It doesn't quite have the "choirs with many, many people" bit, but I recommend Metallica's live album collaboration with the San Francisco Symphonic Orchestra, S&M. It's a collection of live orchestrated renditions of a lot of popular Metallica songs (One, For Whom the Bell Tolls, etc.), underrated gems (Of Wolf And Man, The Thing That Should Not Be, etc.), and two original compositions, No Leaf Clover and Minus Human. It's a really neat experience, listening to reimaginings of your favorite Metallica songs as well as some new, never before heard stuff, so I recommend you check it out.
I didn't quite get what I was looking for with that recommendation (Pantera is 90's, which I don't consider old school at all, and it's more groove metal than thrash metal), so I'll ask again: Old school thrash metal, please, akin to bands like Metallica, Anthrax, Slayer, Megadeth, Testament, etc. Thanks in advance.