Hi Pauley.
Wow, this is a very nice formula.
Just a comment to my problem description. I have only one list of strings and I need to compare each string to all the other strings.
I'm looking for the number of different characters in two strings, so I've modified your formula accordingly: len(string)-your_formula

Now to my test of the formula.
First, I have "copy-transposed" my list (located in column A, starting in A2) to the 1st row (starting in B1). Here is one limitation. The max number of strings will be 16'384, as this is the max. columns limitation in excel, right?. Then I applied the formula:
- list of 7 strings => perfect
- list of 1400 strings => still OK, takes some time, of course, but is pretty fast, I think
- list of ca.11'000 strings => excel at its limits (auto-calculation turned off), producing various messages - cannot finish the job, cannot access the save folder. I think, it calculated the table, actually, but cannot handle the file.

I'll probably try to make some VBA script which produces directly a text file.
Anyway, your solution is so easy and is doing so much. Thanks.
Peter