it really depends on your guitar/pickups/cabinet ..
from my perspective:
I use a 7 string guitar tuned to B standard... My guitar has huge bottom end and has plenty of brightness as it is a wenge cap on mahogany body+ rosewood neck with ebony fillets+ ebony fretboard (lots of ebony underlines presence and harshness) I had some hard times finding the right pickup combination you know
What I usually aim for is a fat rock sound..
I mainly use MK4 mode on channel 3.. I find the extreme more 'metal' but not in a good way.. extreme has pronounced bass and trebles which seems it sounds huge when you play on your own but in a band situation it is somewhat scooped.. (of course, it depends on style, guitar, the player himself etc.)
What I do is that in the first place I disengage the GEQ when I set my ch3.. I set my treble and gain both to 2:30 (o'clock) my mids are 11:00 and my bass is completely down like.. on 0.. the more gain you use, the less bass you should be using... the less bass I use, the tighter the sound gets.. If I had another guitar and wanted to readjust my sound I'd probably only touch the bass knob.. Usually I just play a random djent djent djent on the upper bass B string and listen to the sound if it gets too round I back it up (actually the only applicable setting for my guitar was that mentioned 0
)
I keep my presence on 12:00.. and I have the bright switch on.. The thing is that if I do not press the bright on the sound gets 'fuller' but in that way that I loose string definiton and 'gain'.. lets call it sensitivity.. Presence, gain and trebles+ the bright switch are the biggest factor to achieve more juice but at the cost of stressing upper mid spike and piercing trebles..
Then I set the GEQ to my liking.. I set my sliders to a V shape but I keep the 750hz fairly high ( i dont scoop the hell out of it cause i dont want a thin djenty sound) it's only a tiny bit below the middle line.. What I keep almost flat on the middle line is the last slider.. this is the one that underlines the 'buzz'.. first two sliders determine the fullness of the sound, yet again, you have to use your ears to adjust..
this means that if you think the sound is too bright/harsh I would disengage the 'bright' switch.. if it is still too bright I'd back down the presence knob a bit..
what I found out that so many players who use mk5 think that ch2 and ch3 are somewhat unlinked.. like.. two different sounds that do not combine well.. mine are not..
the key to approaching a similar homogenous sound on both channels is to use the GEQ on both ch2 crunch and ch3 mk4.. actually my settings for ch2 are very similar to ch3
the funny thing is that I find myself mostly on ch2 playing the stuff we play, cause it sounds slightly fuller and more 'hard rock'.. in certain situations where i need tightness and compression i hit ch3 and there we are
oh and one thing.. the sizzle is really there in all cases and in band situation it is your friend.. you only need to find the right amount.. I find the sound on the mk5 impressive, I'd say I don't like my sound that much when I play on my own but in band situation, it's very very articulate and it does not compete with the bass sound, toms, vocals or cymbals.. it sits in the mix so well..