Large volume is defined as more than 1000 per month.
1. The client should probably use the GL as the destination as with that type of volume Concur is probably paying for everything
2. If they have only a few extracts per month (with lots of reports per extract), it might make sense for them to use the Extract API (rest of setup just like InvoiceConnect) choice in settings
3. If it is still taking an extremely long time to run through an import, they can shut off the ReportDetails.xml logging by putting the following in their Brittenford.AppSettings.config file (and restarting GP)
<add key="SaveReportDetails" value="1"/> <!-- 1 save nothing, 2 save only failed, other save all -->
Taking these steps will allow EC to run much faster and use less memory. However, these steps should only be taken if needed (as a last resort).