Style of metal matters a bit here, I think. I like older-school stuff (Sabbath, Accept, etc) and find the S-100 to be really good for this. I probably get a better sound out of it through my Laney AOR than I do either of my Flying Vs. There's a lot of meat in that tone.
However, if the goal is really blazingly fast, something like a Jackson has some advantages. I got a chance to try one through an Engl amp, and it is more suited to really high-gain death metal and very high speed rhythm, in that there's not a lot of low end, and the guitar has tons of attack.
Me, I compromise, and play the Guild or a V through the Engl.