Re: P-Rails in a RG370DX
Okay, I'm very biased on this subject, but I've got these in a 540S (HSH), a Yamaha Ty Tabor model (HSS with Duncan Tripleshot ring), and I'm in the middle of putting them in a strat. I love the versatility and honestly expect some noise out of any tapped coil. The humbucker in parallel is just awesome. I like the single and P90 sounds too, yes the P90 especially can be noisy, but that's what p90s are, overwould single coil pickups, so you're going to get some noise.
As for setup, my 540S is setup to do either coil or just in parallel and the Tripleshot mounting ring on the Ty Tabor gives the options of either coil, parallel, or series. In the strat I'm going to H-H with a 3 way toggle replacing one of the Tone controls for p90-Humbucker-Rail selection(I've never like the 2 tone controls on strats anyway) and a push/pull on the other tone control for series/parallel humbucker.
The best info (albeit somewhat biased) will be on the Seymour Duncan User Group Forum - they have a lot of wiring schematics and opinions over there. Also, Jemsiter FrankFalbo is an excellent resource.