..for my Epi LP standard. At the moment, I have two in mind for each pup position.

For bridge: Dimarzio Evolution 159 or Seymour Duncan SH-4.

For neck: Dimarzio Evolution 158 or Seymour Duncan SH-2.

I play through a marshall mg15, and I know that the pups aren't really going to improve the sound. But I'm looking at this as an investment for when I get a better amp, which will probably end up being a Laney or an Orange.

I'm looking for good all-rounders - something that has clarity and definition on cleans, handles high gain well, and has a bit of a chunky sound. I was thinking before about mixing and matching (e.g. the 159 for distortion and the SH-2 for cleans), and the only thing I'm a little concerned about is the volume difference, as I know the Dimarzio Evolutions have very high output (not sure about the SDs).

Budget isn't an issue.

Opinions? I'm happy to clarify anything if you need more information.
It won't really be much of an investment if you can't really tell what your guitar is going to sound like with those pickups into the amp you're looking to buy.

Buying pickups can be really finicky, because they're always going to sound different depending on the guitar they're in and the amp they're being put through, and even if you splurge on a set of high end pickups (lets say... $300+), there is no guarantee that you'll like how they sound with your guitar and the amp you're looking to buy. So really, buy the amp first, play around wtih your guitar, upgrade pots and caps, and then from there, diagnose tone problems (what you like and what you don't like) and then use that to narrow down pickup choices. I could name about 10 different pickups that are good "all around" but sound vastly different from each other.
Agreed. It's cool to think about pickups now if that is what you are doing. The best advice is to apply all funds toward the amp and get settled in with that before you start pulling the trigger on additional gear. Been there....done that.

You could get a Laney or an Orange and all the sudden your needs change. Otherwise, I think you are tracking and I'm a Duncan fan based on their customer service and exchange policies.

Good luck.