1. Have you tried roughcast A5? I prefer it to UOA5. You might like to compare UOA5 in the bridge pickup of one guitar and RCA5 in the bridge pickup of another. I have and that's how I noticed the discordant harmonics of UOA5 compared to RCA5.
2. I really like RCA3 for clean tones. Beautiful clean tones. But for the way I play, the lower output makes it less suitable for overdriven solos compared to A2, A4 or A5. I love using A3 for clean chords from the neck pickup and RCA2 in the bridge pickup for more overdriven tones.
3. I go back and forth about A4. I think I prefer it in a bridge pickup with A2 in the neck pickup. I do have a PRS with two A4 pickups but it's not my favorite sound. I also have a set of A4 Tom Holmes humbuckers in my Gibson ES-335. That's a fairly resonant semi-hollowbody as you know. A4 sounds better in it than it does in my solidbody PRS Singlecut. A4 is the magnet most often used in real 59 Les Pauls, according to Tom Holmes. When he worked for Gibson he found invoices for magnet purchases in 1959 and he says that's what Gibson purchased most. That may be, but I prefer RCA2.
I do prefer roughcast A5 to polished, though I've found the difference to be fairly subtle, far less change than a swap to UOA5.
Also own a couple of old Duncan 59s with the black US- made mags; these seem to sound more like roughcast than the newer ones do.
I'm interested to try A3 in a stronger wind. It really does lack power in PAF winds - that's why I've only tried it in neck pickups so far.
Someone hereabouts once posted that an A3 Custom is nice. I intend to try that someday soon.
I too have mixed feelings about A4. I have factory McCarty pickups in one of my PRSs; they're just okay. The guitar is all korina and very lively so I think it should have a ton of personality, but it takes a fair amount of gain before its true colors begin to shine with the stock A4s.
I find the A4 Holmes set head and shoulders above the McCartys. And I have a Wizz A4 set that really woke up a fairly lackluster guitar. Which has led me to the opinion that A4 likely is pretty sensitive to the coils as well as needing the a good match in the wood. I agree with the general consensus that in the right situation it can sound downright godly, but that it can also be pretty picky. Maybe more forgiving in neck position IMO.
As for the original PAFs with A4, the best of them of course are legendary. And they're nearly all in good wood by now. Yet I also have a sneaking suspicion that their reputation for tonal unpredictablility could be due partly to the finicky character of A4, and not just their famously inconsistent coil pairings.
I do like a 9K-ish bridge pickup with A2. I've got a Pearly Gates Plus with A2 in it; that one sounds good enough that I intend to swap an A2 into the PG+ in my Showmaster one of these days. I hardly ever pull that guitar out though.
Also have a JB I've been meaning to send to the Customshop so MJ can wind it to '78 specs (or maybe S-Deco, I haven't made up my mind yet) for bridge position on another PRS.