with duckbucker and vintage rails 250k is the norm, for lil 59, JB Jr, cool and or hot rails most people go with 500k...BUT I woudl think that you could do 250k with a CR and be ok...
I have used a JB jr and preferred the 250k and 300k pots, but that is personal preference for sure. I just like the richness when using 300ks with the JB.