I've been testing this over the last few days.

I'm yet to notice any difference it is ever so snappy for me.

caveat is, I'm using my personal xtra account which was created a few months back purely for testing. - Low email volumes.

The trait i'm seeing with those of you facing the issue is, large inboxes.

That is not to say a large inbox is the problem as for a user experience i would expect it to be able to reasonably handle things.

i'll keep testing, however i may end up needing to get my hands on a larger inbox to replicate the issue.

@jaybeedee please confirm how many emails you have in your inbox (rounded is fine), this may support my running theory.