What speakers? Anyway, the reason the neck pup would be useful is because you're wanting a smooth lead tone. The neck position is always going to give a smoother tone. I don't blame you for not liking it for rhythm, as with high gain all you'll mostly get is undefined mud. But for lead tone, it doesn't even matter that much what pickup you put in the neck IMO, as it will always get a decent smoothed out tone. With the RR24 being a very bright guitar, I'd head toward a warmer pickup, which won't necessarily make your rhythm muddy because of so much brightness (alder/maple/neck-thru/ebony/FR) that the pickup will be contrasting with, and it will smooth out the lead tone. The Air Norton would actually be a pretty good choice, as well as the Tone Zone, just based on how they will balance out the RR24. Both of them are alnico-based, which is probably what you should end up going for. The X2N and D-Activators would IMO be too harsh and treble-y (and are both ceramic-based). Also though, if you haven't ever tried an EMG 85 (also alnico-based) in the bridge, I wouldn't give up on actives just yet, especially since you are using a 5150. With a good tube amp, actives can sound amazing. It's low-end tubes/Solid States/PODs that most people will hate actives in, and rightly so of them. Also, many people who dislike active pickups are thinking of the EMG 81 specifically. I have an 85 in my Edwards RV and it rapes buttsecks. The 81 can sound good, but it takes more work EQ-ing it just right because of the very flat response it gives (precisely what actives are good for, and the reason a lot of people hate them, but also the reason that they can do so much if you know what you're doing with them). The warmth of the 85 balances out the brightness of the guitar, whereas the 81 in that guitar is hard to deal with IMO. I don't really know why EMG 81's are put as stock pickups in bright alder/maple/FR guitars. They are generally much better suited to mahogany-bodied guitars.
I'm also using a 5150 (combo version) btw.
-edit: Also though, I'm not a huge fan of really high output passives (Tone Zone). With a beast like the 5150, you have well enough gain, and I don't see the need to have such a high output pickup. They're more suited for people who mess with the volume knob a lot (which I don't and I assume most people don't) to play with versatility of sound by, but if you really want versatility I'd go with actives.
If you've got a good EQ pedal, I'd recommend the Seymour Duncan SH-5 "Custom". Works fantastically with high-gain amps. It is ceramic-based and balanced/slightly bright though, so that's why I say use it with EQ so you can boost up the low mids. It's what Emppu from Nightwish uses btw, as well as the LoG guitarist AFAIK.