not too old Gibson in the high 7k's are good, the current ones are too hot, very dark
depends on the tone you want... maple necks will stand a bit higher winding, while a mahogany neck seems to like a lighter winding. Definately lighter on thinlines.
Over the years, Gibson has done these well over 10k with alnico 5, 3 and 2, or as low as 7k with the same magnets - depending on what they were making. When they did the thinlines and archtops with P90's they were lighter wound, when they evolved into a "second rate" pickup for low end guitars (solid body) they got hotter, then lighter again as the vintage market heated up, now it seems heavier again for the likes of the BFG and other guitars of recent mfg.
Fralin does a hell of a job on P90's and if you call them, they'll work out a custom wind just for you.