Re: What pots for P-90's?
When I replaced the humbuckers in my Les Paul Custom with Vintage Vibe Guitars full-sized P-90's I went with a direct swap and kept the 500k pots.
To my ears it got that perfect P-90 tone and I didn't feel like I needed to really tork with anything that would change it.
BTW....the Vintage Vibe P-90's are a stunning set of pickups. Hand-wound and well worth what he charges for them (well below what most others do).