Recently I have installed a pair of Bartolini P2CBC soapbars. I used 500k log pots for neck and bridge volumes, and a 250k Fender no-load pot for the tone (it gets bypassed on 10).
Based on my experience, this pickups work fine with 500k pots. The only issue I have is that this wiring works just like a 3-way switch. When I slightly roll off one of the pickups, it is the same as if it was fully rolled off. If you intend to use a vol/vol wiring, use linear pots, or install a single vol and a 3way switch.
I have no experience wiring blend pots so I can't help you on that.