My advice is only second hand from a pro tube dealer I use from England. I own the Siemens 6922 but not the CCa but even the standard West German one is perhaps the best of my growing collection, I just purchased a A "Marconi" = Mullard E88CC. A very different sound indeed. This is what he had to say on your question:
"The gold plated grid posts ,the pinched shape and the scarcity probably increase the 'tube ego' of the owner rather than please the user with the sound ;) I can't remember if I mentioned it before but I am certain one of the favourite 6DJ8 Ihave tried was the CV2493 otherwise known as theE88CC-01 . These were actually made to be better rather than selected like a CV2492/E88CC/6922/CCA"
That being said I have yet to find any CV2493s for sale-
"The gold plated grid posts ,the pinched shape and the scarcity probably increase the 'tube ego' of the owner rather than please the user with the sound ;) I can't remember if I mentioned it before but I am certain one of the favourite 6DJ8 Ihave tried was the CV2493 otherwise known as theE88CC-01 . These were actually made to be better rather than selected like a CV2492/E88CC/6922/CCA"
That being said I have yet to find any CV2493s for sale-