Had a wonder round the boat park at castle cove with a tape measure. hopefully this is useful to someone.
I've collated this data, (i did Marmites measurements wrong, can you re measure please Paul?)
Data i took was the usable track the jib car can travel on in a straight line(so outer stopper to outer stopper) then forstay attachment to one of the jib stoppers (Not the middle, see comments about Marmite)
as you can see, Shinys jib car is quite far outboard, where as Usagi's is a lot more inboard, but further aft.
I will leave you to decide what is best.
PS. Happy to add more boats is people can measure and send me the info.
(Hopefully this one will work)