Re: Black Winter or Nazgal in a RR1?
That's at least a third vote for starting with the Invader!
OP, like you, I'm a huge fan of the '78 and RTM. Both of those are easily in my "Top 5" favorite Duncans. However, neither necessarily offers a bigger low end than the JB (debatable, I know...the voicings are a bit different overall). If you do want a Duncan in that ballpark, I'd suggest taking a look at the PATB-3 (Blues Saraceno model) before you go spending Custom Shop money on one of the others. It has a similar voice and feel to what you already like and was actually designed to warm up thinner sounding guitars.
On that note, the Frankenstein pickup (made for EVH by Duncan) is also a really nice option. I hesitated to recommend that (or its cousin, the Custom Custom) earlier because it seemed like you wanted to keep the power of the higher output pickups. Knowing you like the '78 and RTM, however, you might really enjoy the Frankie.
The GL Hunter is designed to be a less compressed take on the regular Distortion. I doubt that's what you want given your previous experiences.
If you go full Custom Shop, I'd still steer you toward the El Diablo. That's what I think about when I think "crushing" tone. It's very articulate, warm where it needs to be and the compression is highly controllable with pick attack. The sound is really balanced, the bottom end is firm but full and it sounds really good split, which I recommend taking advantage of. Tony Iommi, Dan Donegan (Disturbed), Kevin Bond (Superjoint Ritual) and Scott Ian have all used it as their "signature" pickup. Those guys are all heavy hitters. If you don't mind "high output" pickups, it really works to cure a thin sounding Rhoads and is built for hard rock/metal!
But I'd still try the Invader first
