I've used five of the Gibson P90s in recent years, and been VERY happy with 'em.
P90's have a bit of historical baggage, and they were made differently at different times and seemingly for different models. There are very bright, yet still powerful 7.5k P90's from the early 60's that I've been told about, and also some REALLY heavy wound - better than 10k units from the later 60's. The light wound ones are sweet and clear, while the heavy ones are very middy.
So when somebody says "I like the P90 tone" they could literally be talking about many different things.....
The current ones seem to be in the lower mid 8's .. 8.2 to about 8.5.
Reversing the phase on P90's is very easy to do, as well as reversing the magnets, so you can get hum canceling in the "both" position. I've done this on a SG Special/Classic conversion.... and it works fine. Similarly, on Vics Tele the wires were separated so phase and series operation could be done.
I like the current 8.x P90. Its got good stout bottom, thump, sprarkly top, even mids. It holds it own on clean and heavy playing. A good mix of tones, and I think Gibson has pretty much perfected it (assuming you want just one type of P90).
Lindy Fralin has some nice P90's as well.... and will wind you what you want. Try something like 7.5k neck and 9k bridge. Keep in mind that Lindy himself is a rockabilly player, and prefers a slightly brigher, sweeter, less middy P90, so "Lindy's Favorite" may or may not suit you (I prefer em a little heavier than he cares for... your taste no doubt will vary as well).