A popular member for large kio ponds seem to be Sturgeon, they are winter hardy and can be tamed just like koi. My dad hand feeds his Sturgeon which also sticks his snout out of the water around the edges of the pond during non feeding times making it quite a character, also not aggresive to other pond mates. only suggested for LARGE ponds!!
Golden Rudd give off fantastic colours especially when kept in large shoals, as well as roach, again a shoal fish.
But one of my favorites is the Bristol blue, which can grow to quite a size within a large pond. With a multiple of colours avalible and fantastic flowing tails these and shubumkins are a must for the garden pond. Variety is the spice of life and the more variety of colours within pond the more pleasing to the eye it can be.