In all actuallity, there is no right answer on either case. I've seen scale boats as low as 8 pounds ready to go(including fuel) as well as in excess of 20 pounds. The differences in performance were in acceleration and stability. The lite boat could outrun everyone but also blew over easily. By and large, the average falls in the 12-15 range for a scale and 4-7 for a sport 20. Prop weight needs to be kept to a minimum but, more importantly, the boat needs to be balanced just aft of the sponsons. If you can keep a majority of the weight forward, added weight can be kept to a minimum and prop weight will be normally in the acceptable range. That is why, in this build, I've tried to reduce weight as much as possible. It's easy to add weight to balance a boat, it's very difficult to remove it from a finished boat