I'll only speak to Pickups I've had in my bird, no mini humbuckers that I tried in my LP deluxe.
I hope everybody can add reviews of the pickups they've tried so we can have the ultimate Firebird Pickup Encyclopedia!
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Stock Gibson (2007) ceramic Neck Pickup: This is a high output pickup that was pretty woolly and borderline muddy depending on the rig. It sounded pretty good when lowered down even with the pickup ring but was only usable for dark jazz-chording or mellow "lush" playing. It actually worked pretty well with fuzz pedals for a gnarly stoner rock fuzz lead sound too. Overall not articulate enough for my style and a little dull sounding.
Stock Gibson (2007) ceramic Bridge Pickup: High output again. If you can dial out the harsh factor with your amp or by leaving the tone knob on your guitar between 8 and 9, this pickup actually sounds great. It's very articulate and responsive. No "blanket over amp" at all. Very clear and drives an amp nicely. It's got a bit of that "hollow / filter / electric slide" kind of thing happening and you can yell into it which is cool. Even still, it is actually stable enough to play high-gain metal without feeding back uncontrollably. I'd like just a pinch more fatness or lowend but it is a bridge pup. Once you add some gain it's not too spikey either. I wouldn't use it for super clean tones but it's nice to have a pickup that can slice through the mix like a telecaster, do high gain pinch-harmonics, but also work well enough in a classic / psych rock setting. Not vintage correct by any means but a great pickup nonetheless. I like this pickup as close to the strings as possible.
Jason Lollar Firebird neck pickup: Well the old saying that a good firebird pickup should have all the best qualities of a single coil AND a humbucker is totally accurate here. Theres so much snap and sparkle in this pickup! If I am playing super clean the high strings are as bright (though way way thicker) as my bridge pickup when I snap them using a hard up-strum. This pickup is all about body and clarity. I was initially a little underwhelmed until I realized I had it way too low. Once I raised it very close to the strings it came to life. This is a great blues / rock / general playing pickup. It is very stable with high volumes an gain and has a very full range sound. This is definitely the one of the best neck humbuckers I've ever heard in any size.
Seymour Duncan SM-3 Seymourized mini-humbucker: This is a slightly hotter but accurately built version of a firebird pickup. It sounded killer and reminded me of the Neil Young bridge tone. It was a little too conservative sounding for me if that makes sense so I went back to the stock bridge with its massive output. Overall a very strong pickup that would be great for blues / slide / rock / traditional firebird tones.
. For MY use...useless.
