Amongst the "top artists" in the genre listed here and here, besides the obvious (Porcupine Tree at #16 at last.fm, which is on the fringes of the genre as it is), I haven't been all too moved or impressed by much of the others. I look for songwriting centrally, and the heavy guitar crunches/riffs only if they effectively complement it or properly ornament it. I did like one album from Opeth, which wasn't a typical Opeth album, however: Damnation, a soft, non-metal acoustic album (one of the three Opeth albums produced by PT's Steven Wilson). Track #2 ("In my Time of Need"), especially.

Amongst more "grown-up" Objectivists, I doubt you'll find many fans of harsh or grating sounding music, but more interest in softer, song-driven work. (I can't figure out whether it's "melody" or "harmony" people are referring to when I have in mind the way the notes are put together in wondrous, memorable ways.) Metal may have plenty of impressive arrangements of riffs, chords, drums, and so on, but too little in the way of melody/harmony. I think that the more a genre strays from the standards and norms of the classical-music style, the fewer fans amongst Objectivists you're going to find. (This goes for much of "modern" classical, too, BTW; that is, modernist composition has strayed too far from what makes classical an important listened-to genre.)