3 amp more to charge , the difference isn't huge. Now if you went from 6 to 35 you'd have some room for an amp and some subs and maybe some neon lights . Typically the larger amp systems were for power trim and tilt which I don't think you have. You run lights and a ff, 6 amp is adequate, 9 amp is just a little more.
that makes sense now ,i do have tilt and trim. not listed in serial number,but may have been added by previous owner.unsure as i recently purchased from another individual. i think i will stay with the 9 amp.