So, about the weight bit... I'll not comment on the freedom units bit, but my cat is the smallest male out of all his siblings, at 18lbs (~8kg). His brothers, last I heard, are 20, 21, 27, and 29 (that's all in "freedom units", so about 9, 9.5, 12, and 13 kg respectively). His sisters, however, are 13, 16, 19, and 23lbs (6, 7, 8, and 10kg)
Siberians can be huge, though the last two males are a bit overweight. I don't think I'll ever be able to see an "average" sized cat (6~10lbs) as anything but "small" having grown up with two siberians and my friends having other large cats (the smallest being 12lbs, the largest 16) as well as having a close relationship with a purebred siberian cat breeder.