Consider these things too:
For down-picked 8th notes, along with applying less pressure, palm mute power chords. You'll get thicker chunk due to the delay in hitting the second string, and due to the second string not being the root note. May be suitable for a 1-guitar live band situation. on the flip side, may not be suitable for a 2-guitar live part.... that's fast and needs too be tight. Bottom-line, power chord palm muting will be part and application specific. These 2-note palm mutes are how I get the intense djent crunch tone found on such parts as the intro to Milk on Anthrax's "killer b's" album. If you really want to get intense, do your 3-note power chords.
also remember what you're hearing on disc is, in many cases, more than one track and/or single performance on a string(s).