Each practice is a bit different, just as their hardware config is different, but a couple of very simple tests when they complain about performance is to restart their AC services, and ask them if it seems faster.
If that doesn't make a difference, try restarting SQL Server on the AC 'server'.
After doing this for a very long time, these are the fastest ways to check a few things. Part of the issue is you can document ALL of the technical details, or have the end-users give you quick feedback, then dig deeper as necessary.
