Thanks EN48,
With regard to 5 pob, I'm thinking one wife and 3 kids who would only add up to about 290 lb plus me makes a mere 470. So weight is not so much the problem as seats and baggage volume.
Looking at the numbers for the 480B:
Useful load: 1180 lb
1 x family 470 + full fuel 600lb and 110lb left over for baggage!
Not sure what the appeal of the JR was now that I am aware of the 5 seat option.