OK.....so after all the "partial results" are eliminated via the proper
use of criteria, I know for a fact (hypothetically speaking)there are
over 5000 files with my specified search criteria on my
system.....there's nothing left to "add criteria to your query to reduce
the number of results below 5000."
In that case, you would need to do two or more queries, each with added
criteria. For example, the OP's query specifies five different file
extensions and nothing else. He could do two or more queries, each with
added criteria to reduce the number of results. For example, the queries
might be restricted by date:
ext

pst OR pdf OR jpg OR doc OR xls) +modified:thisyear
ext

pst OR pdf OR jpg OR doc OR xls) -modified:thisyear
Or by author:
ext

pst OR pdf OR jpg OR doc OR xls) +author:bob
ext

pst OR pdf OR jpg OR doc OR xls) -author:bob
Or by whatever criteria are appropriate to divide the results into groups
of 5000 or less. The point is that between the queries, all the desired
file types would be found.
Doug M. in NJ