Re: '59 vs Pearly Gates in SG Special
PGs will sound like a spicier version of those stock pickups. The PGs' basic flavor isn't too far off from the 490's. But the PGs will overdrive the amp earlier, so they are creamier...yet they also have a more biting high end floating on top of the cream.
Played completely dry, the 490's will sound more like a classic old-school humbucker tone than the PGs. PGs don't clean up as easily, and when they do, they sound more like over-wound single coils than like humbuckers.
59's will have the power of PGs, but they will sound drier - less "juicy," I would say. They are much more stiff and clattery, with much more anemic mids. However, they have a certain "wall of sound" mule kick character that the PGs and 490's don't have. If the PG is leather whip, then the 59 is a bamboo switch. IME, they are somewhat hard to clean up successfully, because they tend to hit amps relatively hard...but that's probably okay, because if you ever do clean them up, they sound hopelessly lifeless and sterile anyhow.
IMO, the 59's are best suited to being used with healthy amounts of gain and/or effects, and to being played pretty "straight ahead" with the right hand...i.e. at pretty much the same force all the time...while relying more on technology to achieve your dynamics (e.g. pedals or your volume knob). The PGs, OTOH, are more "hands on." They're better for those who rely more on natural amp breakup, and who play more dynamically with the right hand.