Checking a match for numbers

I want to check the contents of a variable for "too many" numbers

I'm sure there's a clever way with a weighted or match

something along the lines of "more than 4 numbers and more than 20% of the =
characters"

(A lot of mailers are now polluting the list-ID header with bullshit, and I=
 want to detect that so I can discard the list-ID when it's garbage)

-- =

Apple broke AppleScripting signatures in Mail.app, so no random signatures.