I've never been sure about how a pickup will sound before I put it in the guitar - I've replaced almost all the stock pickups in the guitars I have, though. My son has an Epiphone Bully SG (cheapest one they ever made, I think), and we put a Gibson Dirty Fingers in it - that one pickup cost more than the guitar. Sounds pretty good, and the Epi plays pretty well, too. If he upgrades guitars, we'll definitely move the pickup to the new one.
In another SG clone, I put a Rio Grande Texas/BBQ set, and they both sound really good.
In yet another SG clone, I put two Gibson P94 (single coil - double coil size) - they're awesome, and very different from the double coil ones.
I've got
a Gibson SG Supreme with 57 classics (stock) - I like them, too - I know they're sold separately. (and for the type of music you mentioned, these might be perfect)
One place I tend to screw up with pickup selection is getting ones that are too hot - then I have to turn them down on the guitar to avoid overloading whatever it is I'm plugging into. The P94s are stupid hot, for instance. One time, I had a Seymour Duncan Invader that was, in my opinion, unusably hot - in fact, the magnets were so strong that it seemed like they actually pulled the strings down and affected tuning.
When I change the pickups, I also change over to CTS pots if they're not already there, and put my own capacitors on the tone pots. I leave the switches and jacks alone for the most part. I'm pretty sure Epi uses CTS pots and generally decent electronics, so it may not be worth switching.
(btw, if you're soldering pots, be sure to solder the ground connection to the pot body *before* you solder other wires to the terminals - to solder the ground connection effectively, you have to heat up the whole pot, and if you already have wires attached, that heat bleeds off into the rest of your system)
All that said.... The stock Epi pickups didn't sound *that* bad. If you're not liking your sound, be sure to think first about what you're plugging into. You didn't say what, but it's worth pointing out that a decent preamp with a D.I. makes a *big* difference over going direct into a computer line in, for instance.