Re: Gibson 57 Classic vs Duncan 59?
I have tried a Classic 57, 57+, and 498t in a Hamer Scarab I own (all mahogany, set neck, rosewood, 500k pots). I haven't tried a 59, but even a Jazz sounds a little warm to me compared to a ceramic neck pup like the EMG 60.
I'm normally an EMG 60/81 (18 volt) guy who wanted a little more warmth for tracking rhythms.
My experience with the 57 is that it is very warm but it doesn't cut through very well. It gets PAF "woo woo" on bends above 12th fret, but it doesn't sizzle, and the notes often pluck instead of sound clearly. It's better for semi hollow, hollow, and jazz, although it doesn't do bad with high gain in Pod Farm 2.5.
I put a 57+ in the neck and it helped a lot. It has more mids and is wound a bit more than the 57, so it cuts through better. Unfortunately, the Classic 57+ doesn't split. The closest thing to it that splits would be a 490t (t since the 57+ is supposed to be used in the bridge--you might try an r). I think they both use A2 magnets and I'm still not sure what the difference is between the 490t and Classic 57+ aside from the splitting and the 57+ having a bit more output.
As for a lot of guys not liking A2 magnets here in favor of the A5, I was pleasantly surprised. When I think of an A2, I think of the bass as being a bit springy and spongy, but this variation also allows you to have pick dynamics. You can vary up the tone by touch a lot, and play with saturation settings. The 57+ was great for that in the bridge--it just wasn't quite firm enough in the bass for me (although it could easily do distorted prog rock stuff like George Lynch). You can always compensate with the amp, though.
I contrast a "spongy" bottom to a flabby bottom, which would be the JB to my ears. The thing sounds flabby, but the flab sounds the same with every attack. In some guitars this might add body, but in all of mine (mostly alder/maple/rosewood/Floyd Rose) it has to be dialed back with a high pass filter for tightness.
As far as matching the 500t, I haven't played it, but to me it depends on if you want a "warm neck/bright bridge" guitar or a "relatively bright neck/bright bridge" guitar.
Some guys like a huge difference between neck and bridge tones for versatility. Others want to be closer matched.
I think if you do a 57/500t you'll have a huge difference. If you want a similar tone to the 57 but with a bit more bite and clarity, try the 57+ in the neck instead.
I've also considered a 496/500t or even a 498t/500t, but I think the 57+ and 500t would be good for you.
My experience with Gibson pickups is that they aren't bad at all, but they are pricey for what you get. Used Duncans would get you a similar tone for a better price. I just bought Gibsons because I know they're only available in a tune o matic spacing and I wanted to save Duncans for if I wanted a PAF tone in a Floyd Rose guitar.