You haven't provided any evidence so far. You owe evidence because you made a claim. If you are unsure whether Bluebird's Promise performance makes a difference in a real-world scenario, why make such a claim?
I agree! But you did answer it:
> Bluebird is mainly designed for node (V8) and promise performance can make a massive difference on the server.
If I'm sacrificing simplicity (by using a non-native Promise implementation with a very large API) because of performance improvements, I want data (proof) of these performance improvements. If you don't have the data that's fine! No harm done, I'll keep waiting until someone does.