The most crushing rhythm guitar sounds IMO are what Jon Schaffer gets in Iced Earth and what Victor Smolski got on Rage's Unity and Soundchaser albums. Jon uses Marshalls with a Les Paul, while Victor used I think a Peavey Triple X for his rhythms (either that or some Yamaha amp, I don't know what he uses for what) and his custom Siggi Braun guitars.
So completely different rigs can get equally awesome tones, just experiment and find what you like the most. My producer hated me for using EMG81's in my guitar, but I love the abrasiveness that they get. Its not very dynamic, but it is very metal
edit: Kreator's tone on Enemy of God is extremely crushing as well.