For the past couple of days I ran a test on a tier 2 context UK campaign because of things suggested in comments to me here: https://forum.gsa-online.de/discussion/9504/slow-submission-few-verified-low-lpm
The setup of the test campaigns was exactly the same bit for bit, except for the email settings which in one case were a batch of 10 hotmail accounts and in the other a set of 10 gmail dottrick randomized emails.
The hotmail accounts outperformed the gmail catchall by more than 2x (i.e. roughly same amount of submissions, hotmail gave me twice as many verifieds). The result based on the sample size had a 99% confidence level (i.e. there is a 99% chance the hotmail accounts will perform much better than the gmail ones).
Will recreate the test again a bit later on a US campaign or if anyone already has, results would be appreciated.