>>Audiofeil, how do you spot a great quality CCa by virture of its sound?<<
That's like asking what spinach tastes like.
To my ears the great Cca are very airy, detailed, and impart a "dimensional" aspect to the presentation. You have to listen for yourself and decide; therein lies the rub. You could put 10 experienced listeners with a series of 6922/7308/Cca tubes and more than likely there would not be clear "winner"
That being said, unless your system is up to the task, it makes little sense to spend money on Cca. I would seek out some lesser priced tubes from the same family; they will give you 98% of a top Cca at a much lower cost. I love the mid 60's Amperex Bugle Boy 6922 for example. Andy at Vintage Tube Service sells high quality products at fair prices.
Know your tube vendor. There is a plethora of counterfeit and junk tubes on the market.