Re: Best Strat pickups for classic rock
Classic Vibe 50's strat should have custom A3 pickups stock. A3 magnet is normally pretty bright with smooth mids and low output. I can't recall anything about that pickup at the moment.
Which switch positions are currently most useful or do you find yourself playing in most?
STK-S9b (or SSL-3 for the noisy equivalent) isn't a very vintage strat sound. If you are comfortable straying from strattiness, it's a pretty nice hot warm sound like a more focused take on a high output humbucker. Probably too hot for your mentioned musical inclinations, though.
If you want warmer with a bit of classic strat still there, STK-S6 Custom (or SSL-5/6) is a better choice, though I'd probably stick with it in the bridge.
For maximum quack in the notch positions, most strat players prefer the brightest/lowest output pickup to be the middle. On the other hand, if you find the notches overly twangy, you might want to replace it with a hotter and warmer pickup like the STK-S7 Hot Vintage Stack Plus.
Depending on how you use things, you might go with a stack in the bridge for reduced noise high gain tones, especially if you prefer high gain from the bridge.
Then you can try other options in the other positions, maybe APS-2. Or if you want twang on low strings, but need less biting high strings you could try a Five-Two (A5 under low strings, A2 under high strings). If you go this route I'd probably replace the bridge first, then the neck, unless you like a more biting neck tone than middle. Then consider whether the remaining pickup needs to change.
One of the classic Gilmour combinations is the SSL-6/SSL-2/SSL-2 (or SSL-5/SSL-1/SSL-1) setup that was already mentioned. Noiseless equivalent of that is the STK-S6/STK-S4/STK-S4 combo, though of course you don't have to stick with noiseless in all slots if you feel they impair cleans as many vintage junkies do.
A popular variation is the STK-S6/STK-S4/STK-S7 combo, gives a warmer, SRVish neck tone without too much hit on the mid+neck quack.
Hope I didn't just induce option paralysis!