I can only answer a few of your questions:

I think that if you saw the production numbers it would be obvious that each year more people (a lot more) bought 5" snares than 6 1/2".

They were cheaper, fit in trap cases better and had the sound most people preferred.

Because of that there's way more 5" ones on eBay, thus the 6 1/2"s are worth more, and they always were.

In the 60's (after the first time Ringo was on Ed Sullivan) Ludwig outsold Slingerland by a mile, so that affected the amount you see today... Slingerland scrambled and year after year, put out inferior catalogs to Ludwig's top notch ones and although their drums were great, today there's way more 60's and later Ludwigs.

I used to carry the Ludwig catalog to school every day with my books in the early 70's. The Slinger catalog mainly had Buddy to brag about, and he wasn't exactly cooperative.

It's pretty obvious that vintage Ludwig Supraphonics in the 6 1/2" depth in nice condition bring significantly more money than those from the same era in the 5" depth.

[COLOR=red]Very true and I agree

[/COLOR]

Is the same true of Slingerland's Gene Krupa Sound King COB snare drums? In other words, would a 6 1/2" Sound King in nice condition bring significantly more money than its counterpart in the 5" depth?

[COLOR=blue]Not significantly but say at least $100 or more[/COLOR]

Also, how would a 6 1/2" depth Krupa COB Sound King snare (10 lugs/zoomatic strainer) compare to a Ludwig Supraphonic in the same configuration and condition?

[COLOR=blue]I have heard people say no comparison, but both sound nice - How's that for skating around the answer?[/COLOR]

Are the Sound Kings in this depth tougher to find than the Supraphonics? I don't see many being offered out there? Also, what would the fair market value be for a 6 1/2" depth Sound King in nice shape, both functionally and cosmetically?

[COLOR=blue]The only reason I posted on the topic is because I have had at least two people in the last few months asking to find this exact drum. They had been looking for a long time trying to find one in excellent shape. I have seen a few dogs show up in the past few months. Usually the 5" is in the $150 - $225 range. (these are ranges!) and the deeper version might be in the $200 - $350 range.

[/COLOR]

Is the sound of the two (Supraphonic/Sound King) even remotely comparable?

[COLOR=blue]The Slingerland is brass and most Supras are not, unless you were originally asking about a brass Supra? .. Hmmm.. More questions...[/COLOR]

As usual, THANKS in advance for your help!

Well............ I guess the question regarding the value of the 6 1/2" Sound King as compared to the 6 1/2" Supraphonic has been answered -- especially if all the Sound King might bring on the "high end" would be $350.00. I've seen Supras in this size go as high as $600.00.

I appreciate the input received thus far!