If you can write the case study so a potential customer feels like you’ve just pulled up a chair and chatted about a story, it will be very effective.
A case study is much more likely to be a genuine “customer testimonial.”
Remember how people in meetings react to a speaker who drones on and on, reciting facts in a monotone.
The criteria a white paper conforms to are much closer to academic standards than to marketing standards.
If you’re going to create a white paper, it needs to provide the best information available.