Marcus, I'm primarily a rhythm oriented guy and I've pretty much ditched all of my EMG's for various passives, mainly Dimarzio's. Here's a list of the pickups I've used for rhythm tones that made me happy:
Crunch Lab: Rolled highs, decent mids, very tight/articulate, excellent chunk with a cool snarl (crunch I guess) that gives a pretty aggressive voicing. The rolled highs make it a good choice if you're like me and don't care for overly bright guitars, or if you want to tame a bright guitar a bit.
D-Activator: As Melb_shredder mentioned, this one is VERY suited to metal riffing. It's like having a pickup with the vibe of active pickups (tight, aggressive, compressed) but with the added benefit of passive pickup cleans. It's much beefier than the EMG's I had, great pickup. I don't know if it's my amp (Coreblade) or the fact I set my pickup height fairly low but I get excellent cleans with them as well.
Dominions: Here's a new set I picked up recently. Tons of mids, more moderate/high output (like a hot PAF), thick but tight tone, great clarity. It's NOT a firebreathing monster of a pickup though but I'm kinda more into moderate/high output instead of monster output pickups these days.
Super 3: High output, TONS of mids, one of THE classic Death metal pickups of the 90's. It's a crusher, I loved that pickup for many years. It's thick as hell but as mentioned earlier the bottom end is plenty tight. It roars like a caged animal. Good stuff.
X2N: **See Chuck Schuldiner** The thing about the X2N is it's dependent on the body wood you use. In a brighter wood it will have more cut, in something warm like mahogany it turns into a sledgehammer. I have one in a SG and it's thick, that's my br00tz guitar.
That's a short list. I've used a ton of other Dimarzio's in the quest for tone but those will get you started. I'm also a Seymour Duncan fan so I don't really see an issue with getting heavy tone with a variety of pickups from different manufacturers. My main reason for liking Dimarzio a bit more is I find some of the models just work for my riffing style a bit more than the Duncans do, mainly in the clarity/tightness department.
As for your question about screws/slugs yes, that apparently does make a difference in tone according to the dudes on the Seymour Duncan forum. Those guys mod their pickups all the time and changing to larger screws apparently add more treble, etc. I don't know all the details on that but I have swapped magnets in some pickups and it makes a difference. I hope that helps dude.