UPDATE:
OK so this is the
FINAL update. After I put two A5's in the Hot P-Rails, it sounded really great.
I just couldn't help myself (I really did try to resist the urge, but I had to try it anyway).
I took out one of the polished A5's and put in an Unoriented roughcast A5 next to the rail. OMG!!! Blueman was right. Even though it was just one of the A5's that I replaced, it sounds much fuller, stronger, boosted up the rail and parallel settings, and made all of the settings match much better. But it's not like the A8...not as overbearing in tone and output, more subtle. It didn't seam to make the series setting any darker, that I can tell, so everything just seams to work together more harmoniously: Rail-Parallel-P-90-Series.
The P-90 is like a sledgehammer and sounds better than any other pup I've played. It's strong/powerful, full-bodied with GREAT mids, and still has that super P-90 bite. The Rail is still bright like it should be (next to the bridge), but with some great overtones to make it sound more organic, more alive. The parallel setting is airy, clear, bright, kind of acoustic sounding, a bit stronger/louder than the Rail by itself. The series setting is very strong, definitely humbuckerish, but not dark and muddy like it was with the stock A8's, very powerful but not overbearing when compared to the P-90, It is a very good bridge humbucker and goes very well with my Classic '57 neck pup.
The P-Rails Hot is very....well.....as you would expect,.........HOT!! It does tend to sound a bit overdriven (especially when it was stock with the A8's, but not as much with the A5's in it). But it cleans up fine with a bit of the volume rolled off.
This is the way it should have been made by SD in the first place, or at least with two polished A5's. The Unoriented roughcast A5 just added the perfection that it needed.
So now I've got great tone, great versatility, and great fun.
I'm so glad I learned about mag swapping on this forum. It transformed a very disappointing initial experience with the Hot P-Rails into perfection. All I can say now is..."WOW".
(Now I'm
really having a hard time deciding which is my favorite guitar...this LP Classic with P-Rails Hot A5/UoA5 (b)/Classic'57

, my Epi LP Ultra with Mean 90 A5/A8 (b)/Pearly Gates

, or my '66 Wilshire with NY Minihumbuckers).
I also still love my Am. Deluxe Strat HSS, too.
Oh, woe is me.