I own several grey label IBM Model M keyboards, as well as a Customizer. Honestly...not that much difference in feel. The bolt modded keyboards feel best, then the Customizer, then the unmodded Model Ms.
And the case artifacts are present on all of the cases, to one extent or another.
To me, the biggest issues are bolt modding, spring age, and key type (one vs. two piece keys).
My cat definitely prefers the Customizer over the IBMs. Not sure why, exactly.