That's really tricky to answer without the policy backup file to inspect as well but historically the type of slowdown you describe can also be attributed to having large amounts of classification type rules in the policy.
Switching off items in the Client Config may help indirectly if they cause the classification not to be applied or not used on files touched by the OS and applications. It's just one scenario of many.
Logs are your friend in these cases, as is the DLP Diagnostic Tool and ProcMon. When a slowdown occurs reproduce with the Diagnostic Tool open and examine the Processes tab and if using tags look at the Data Flow tab. This will give you a feel for the amount of work DLPe is doing.
If that does not tell you anything sensible then repro with ProcMon running. Filter on the FCAG and FCAGTE processes and see if they are accessing huge amounts of Office files (you can see if they are reading by looking at the details column and checking for an increasing 'offset').
More thorough investigation can be done by McAfee support with the aid of an Agent Dump generated from the Diag Tool.