One pickup I'm a huge fan of is the Ibanez Super 58. I have them in my AT700 and it covers everything I want, from light dirt to metal. Great pickup you'll have to find used.
I've run Duncan Customs (the 7-string version) with the stock ceramic magnet, with A5s, and with A8s. The A5 definitely has a bit less punch and balls and a lot more juicy-ness, but the A8 to my ears really is the perfect hybrid between the two. Still great punch and bite, but noticeably more juicy-ness and depth than the stock ceramic. I run A8s in most all my pickups now. For reference, this Custom is in a mahogany-body, maple neck + ebony board locking-trem 7-string I built; playing high-gain stuff through a Bogner and a Boogie.
There's a magnet company that at least used to sell humbucker magnets on Ebay. If you're good with technical stuff, you could snag one, pop it in your Custom, and try it out for only ~$15 and an hour of work.