Will there be a slight pause in data entry compared to pre-Audit Trail on the user’s point of view?
Since Audit Trail Classic is not run during query and export users will not experience any slowdown at that point. Even when they come to enter data they won't experience any slowdown either. If you are able to measure such things you may notice a minuscule increase in time to open and save records but it really is not noticeable.
The only area where you may notice an issue with performance is on import. The process does work slightly slower due to there being multiple records being opened and closed not just one. That being said this depends very much on your hardware. There are also options to switch off the audit during import if you should so wish.