Shubunkin size

My pond's hitting 1 year old next month and I'm in my first summer of
enjoying all the plants and wildlife that it's attracted. At the moment I
have 5 blue shubunkin, 2 koi, a couple of orfes and about a million
stickleback. I knew the koi would grow but my concern is the shubunkin's
growth, 2 of them have gone from around 4 inches to around 8 inches in less
than 4 months and I was wondering what size they generally get to and how
quickly? I'm already looking at the garden and planning a pond extension in
my head but I would like to get an idea of when to start the groundwork on
my girlfriend.

Thanks for any info.

D