I know what I always considered a large border collie. Jinx is 57-58 pounds. He's in fantastic shape and a sport dog owned by my parents' neighbors. He's a beautiful dog, but almost twice as big as normal.
I have an ABCA registered 11 month-old smooth-coated male at 65 lbs with a half blue eye from a saddle and a blue merle, out of a litter of nine. The parents are working cattle dogs in Arkansas and his siblings are similarly tall and lean. The dog is exercised three times a day, two walks and a run, eats about three cups of high protein dry food daily, with liver and hard-boiled eggs during the week. He thinks fast moving children are escaping sheep, does the approach-lie-down-stare-wait at oncoming dogs and people, and learns commands in minutes. He was registered 'Possum' by the breeder, who said he was the shy one of the litter. All this to say, in the US at least, there seems to be not only a wide variety within the breed of coats/color, but of size as well. Maybe there is a need for American BCs working cattle to be larger than their sheep-working counterparts in the UK.