My Mark IV is not quite as sensitive to knob movement as others that I have heard. For example, I can turn the lead channel treble knob from 4 to 6 and not see as dynamic a change as others seem to see. But, I do find that the GEQ can be very sensitive in how it responds.
Having said all of that, my Mark IV is the best amp that I have ever owned. While my LP sounds decent through it, my SG is my guitar of choice.
Channel 1 with the SG gives me some of the best clean tones that I have ever played. I keep bass set arount 7, treble around 6, and mids around 3. I don't use the GEQ on channel 1. And, turning up the gain gives me a breakup that I can control with my pic attack.
For channel 2, I have to pretty much swap settings for the mids and bass. I keep the gain for channel 2 on around 8 and the treble pretty much around 9. With my bridge pickup on the SG, this gives me a really good rhythm tone that is still articulate enough to allow some lead runs.
Channel 3 is where the magic happens. I like using both pickups, with the tone for the bridge pickup turned all the way down, and the tone for the neck pickup turned all the way up. I know it sounds weird, but I get the thickest, nicest lead tones out of that. Plus, when I play lead and pic on the neck itself, it gives some very cool tones.
The Mark IV is heavy. But, mine has side handles. Makes it very nice to pick up.
I don't play metal, so I can't speak for it. But, my Mark IV can handle anything else that I need it to do.
Like I said earlier, best amp I have ever owned.
