IMHO the differences between Quercus and CKone are not subtle. Quercus opens with a much stronger citrus hit. It has a far denser spicey background to it than CKone, and it doesnt wear off about 5 seconds after putting it on.
SImply smelling superficially the same at first sniff, does not mean they are one and the same thing.
Opus is properly delicious though, and if i could only have one fragrance to wear for the rest of my life, this would be it. Its classy, elegant, peppery, herby, spicy all in one. Its such a wonderfully layered smell, and a proper classic. Love it. Well worth having in anyones collection.