Re: JB mods
I completely agree with you (Megadeth is my favorite band

), but I also play Pantera. I'm a fan of the JB, I just need to be able to get a little bit more chunk. Putting a ceramic in helped, but I miss the A5's sound a little bit, it was a bit more 'organic'.
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If you like it with ceramic, but want to tame the present bite, A8 is definitely a good place to start. Allen heads, particularly under wound strings, are great for not just tightening the bass but more aggressive attack.
Note that you can get both roughcast and unoriented on the same magnet. For tight bass, I wouldn't be surprised if you prefer RCA5 to UOA5. Unoriented A5 is generally considered to behave like a blend of A2 and A5. Can get RCUOA5 too, though...
A2 JB has it's fans too, even in metal. Warren DeMartini for example.
Don't be afraid to experiment. I've found I love hex heads under the bass strings, but prefer keeping the longer, stock screws under the unwound strings for more mids/smoother high end on them. Punchier attack on bass notes, smoother on leads. Referred to variously as half-hexed or hexed bass.
My old Ibanez RG570 guitar hated my JB in the bridge, weird flubby lower mids AND piercing one-dimensional upper mids. Great for leads, horrible for almost anything else. I replaced it with a PATB-1b, which I really like. Just as amazing for leads, but vastly more flexible, better for the whole gamut from clean to distorted chords.
Then I started hating the stock neck pickup even more. I wound up putting A3 in the JB, hexing the bass and using it as a neck pickup with a few setup tricks [studs towards neck, screwed close under treble, down under wound, string volume balanced by raising screws progressively toward wound strings].
Once I got the height/screws adjusted, it sounds sort of like an A2 JB does as a bridge pickup, but beefier. Weirdly, both fatter and tighter set up like that than it was as an A5 bridge pickup. And yet has more sparkle clean, despite being really meaty. Unexpected blend of squishy and punchy feel. Volume balances quite well against the bridge A5 pickup, which I was a bit worried about.
Still haven't gotten around to trying a different neck pickup. And it's nice that everything I did to the JB is readily reversed, should I decide to swap it for something else.