Re: Replacement for Jackson J-100
I'm surprised you didn't go for the STK-S6 or SSL-6 instead of the SSL-5 (Hum-cancelling version of the SSL-6, which is the flat radius instead of traditional stagger of the SSL-5). Unless you've got a small radius fretboard, the flat radius gives better string balance. Though some people love staggered FOR the uneveess. Of course, a lot of those are Hendrix tone-chasers who should be using a left-hand stagger on their right-handed guitar.
I'd have suggested it in this thread, but I figured you'd already read the other thread about Jacksons you posted in. Though given your tone description, I'd have figured you'd go for the STK-S4 (or SSL-2 or SSL-1).
Stacks are single coils, as far as tonal applications go (there's some dispute over how close they are in tone, I feel that the difference in tone is almost entirely from the lack of noise in the newer designs like the Stack Plus line). A lot of people don't like single coils for lead tones with heavy distortion, but many of them haven't tried hot single coils, either...
Anyways, alternate tone for an SC-sized slot would be a single-sized humbucker, still a side by side humbucker, just narrower. Like the Hot or Cool Rails pickups, or the Little '59, Little JB, etc. They get an odd sound, with a focus a bit more like a single than a full-sized HB, but tone a bit closer to the HB.
Anyways, hope what you ordered works out for you (or that you are somewhere the 21-day guarantee is available). Please follow up with comments on how it worked (or didn't) for you!