I'd go with 500k pots. Bareknuckle's wiring diagram for two P90s shows 500k, and that's what Gibson use. And with the higher DCR of the 'Pig 90, you want 500k to get as much brightness as you can, otherwise with 250k pots it could get quite muddy sounding.

https://www.bareknucklepickups.co.uk...sp_bd4beb2.pdf