"If you're testing your SQL with and without indexes to find the right combination, be sure to close out of FoxPro between tests to eliminate the caching."

The OS will also be doing plenty of caching, both the Workstation and the Server (if one is involved). The bad news is that a categorical picture can only be obtained by cold boots all round between each test!

If you are using NT4 / Win2K you should also consider using PerfMon.Exe or the Task Manager - with the Process Tab selected, select Select Columns from the View menu, and enable both Page Faults and PF Delta. If you see large values in the PF Delta during the first run, but none or few during subsequent runs, then your queries are faster the second time round due to caching.