Your question leaves a wide range of pickups. First of all, you've got to decide what kind of power you want in a pickup. The thing is, strats aren't as resonant as Les Pauls, so generally you need a bit more output. Check your pot values. If you have 250k or 500k pots, that will make a difference. Check sparkguitars.com and you'll see that my builds have all different pickups, so I know humbuckers and strats very well. Moreover, I've done a LOT of pickup swapping, magnet swapping, and even a couple of hybrid conversions. Even knowing all this, I can hardly give you recommendations without more information.
First of all, you said heavier rock/shred, so I'm going to assume that you're not really looking for death and destruction pickups like the X2N, Nailbomb, Nazgul, or something. The pickups you mentioned are med-high output pickups. If you want to shred, then you definitely need something that has character, dimension, definition, punch, and not too much compression. Basically an expressive medium to medium-high output pickup.
A second consideration is the magnet type. Your most basic options are Alnico and ceramic. Alnico tends to have a flavor while ceramic is kind of colorless. Pickups with ceramic magnets typically have more output than Alnico pickups. Ceramic magnets typically have more definition or less mud, which is another reason why they're used for metal. However, guys like Schenker used high-output ceramic pickups to drive vintage amps. There is something really great about the way high output pickups drive an amp.
That's another consideration because there are basically two ways to go about it, drive your amp a little or use medium to low output pickups that don't push your amp. When you drive your amp, it compresses a bit, so for shred, you want some compression but not too much. You need that openness because it lets the notes sing and the dynamics don't get compressed.
That's another thing. What kind of shredder are you? If you're the kind who mostly picks notes or mostly uses legato, either style makes a difference. For legato, you want more punch and output so that you don't have to work too much for sustain. For picked notes, you need some quack or snap so that you can hear all the notes flutter as you speed around. Pickups combinations like the Dimarzio Norton/PAF Pro, Duncan Custom Custom/Full Shred, Bareknuckle Mule/Riff Rafff are all excellent for both picked and legato runs.
Pickups like the Dimarzio Fred, AT-1, and Bareknuckle Holy Divers are very upper-midrangy and kind of bright, and they have pretty good output, so that makes them very good for legato. Legato tends to have a warmer attack than striking the notes with a pick, so brighter pickups may be better. Hot pickups aren't really that good for legato because it's much harder to get dynamics from legato than from picking, so you don't want too much compression.
From what I've learned over the years, it's not always simple buying pickups. It's like buying the right speaker. You really need to know what you want to achieve with it and what compliments your gear. Pickups respond to wood, coated/uncoated strings, fret material, etc., so you want pickups that either compliment the components or augments them in some way that achieves a desired effect.
What this means is that if you have say an ash strat with a maple neck and ebony fretboard, stainless steel frets, Cleartone strings, and vintage bent saddles, then chances are your strat will be on the bright/snappy side, nice deep lows, and more balanced midrange. Alder, for instance, would be a bit warmer and thicker in the mids. Therefore, you probably want a pickup like a Dimarzio Air-Zone or Duncan Custom Custom. If you installed say a Bareknuckle Holy Diver or Dimarzio Steve's Special, then you'd have a very bright guitar.
One the flip side, let's say you have a basswood strat that lacks a bit of low end and has a warm high end, but you want more low end and brighter treble, then you'd probably choose something like a Dimarzio Tone Zone, Bareknuckle Crawler, or Duncan PATB-1. Those pickups would augment the sound of your guitar to give you a bit more of what you want.
Having said all of that, I'll generally give you some suggestions which comfortably fit in the "strat with humbuckers for shred rock" category that are good for alternate picking, legato, riffing, and still sound good clean or mildly overdriven. Here are some models from the most common brands that I'd suggest:
Dimarzio Air-Zone/Paf Pro
Dimarzio PAF Masters
Duncan Custom Custom/Full Shred
Duncan Pegasus/Sentient
Bareknuckle Mule/Riff-Raff
Bareknuckle Crawlers
EMG H4A (passive set)
David Allen P51 Mustangs
Lollar Imperials
Fralin Pure PAF (8.4k)
