Let's say you are updating a single field on 1000 records, would csv import or mass update be quicker? Is there a noticeable difference in speed between the two methods of updating the field?

If you CSV import, you have the option to not trigger any server-side logic which in theory should be quicker. Mass update will fire an XEDIT event for each record updated.

exactly the type of answer I was looking for, thank you!