I got my Mayones Regius Core 7 with JBs. Never played or had any JBs before. I planned to try them out first and then to swap them if I don't like them.
First they sounded like a mess, definitely too hot and without any definition at all. I thought ok, the Mayones guys don't put JB in their high quality hand crafted guitars for no reason. I emailed the guy from the music store who sold me the guitar and he said he messed with my guitar upon arrival before forwarding it to me, cause he had tuned it "better" than the guys from Mayones (a very decent guy BTW). Then I thought ok, since there can no harm be done now, whatever it was that the optimal original factory setup was, it's gone. Then I started tweaking it to my taste and ended up with the distance of pickups to strings around 6 mm instead of 2,5 mm as I read somewhere as a starting point. It looks strange so low but I found it the best sounding, with right balance between headroom, definition and power.
I can hit the bass strings harder without them sounding harsh, with nice vintage alnico kind of dynamics. Almost like my old '79 Gibson SG. I noticed that palm muting even sounds the best when hit harder. Then it sounds round, full and punchy. The middle and treble were a bit too much until I lowered the bridge pup some more on the higher strings side.
The neck pup sounds almost like an acoustic guitar with this lower setup but nice and even when played through clean presets.
I can say that this is the best 7 string guitar and pickup combination that I ever had. I play also a lot of metal and it works well. Without muddiness that is often mentioned in JB discussions. I know now that a few turns with a screwdriver can make the whole difference and I would suggest doing this with any set of pickups.