I can compare my two G-3s (with stock and modded pup combos) during the day and report ...
(Not much later in another part of the city ...) Ok, did that just now:
My 78 maple board G-3 in ebony is wired stock, i.e. 1.
neck/middle, 2. all three and 3. middle/bridge.
My 82 ebony board G-3 in CAR is wired 1.
neck/bridge, 2. all three and 3. middle/bridge.
So the difference lies in position 1 (not 3 as I erroneously believed to remember). And just as in a stock set up I find the neck/middle combo sounding better than all three together (too much frequency overlap there me thinks), the modded neck/bridge combo
sounds even better as it combines the ooomph of stock position 1 with the attack of stock position 3 (middle/bridge), all very clear, but with authority, think of a forceful Jazz Bass minus the phase cancellation which you can only correct on a Jazz by dialing down a little one of the single coils. There is no volume difference to the other two stock positions.
Having heard all the positions side by side now, I actually think that a modded combination replacing the "all three" stock (middle) position with a modded neck/bridge combo (sans the middle pup) and retaining the neck/middle and middle/bridge (which I like for its no-holds-barred attack without sounding wheeny) stock alternatives would be the best choice.
Have I declarified everything sufficiently?