An A/B test might be interesting, but we have scores from any conference that takes feedback seriously. Commercial conferences will sometimes be ranking speakers on individual tracks and you'll get a pep talk about expectations before and a review after.

I was thrown into one of those conferences with a colleague once and it was pretty intense. I sat in on sessions and had access to the scores and feedback later and people would have very specific things they didn't like about the speaking. Having listened you can sort of agree with the attendee, but access to formal training, or a good mentor can be tough. Former employer offered an hour with a speaking coach at one point and that made a big impact on my issues, but people don't give similar feedback in the local dev speaking circuits.