For a customer having 12K+ users with anybody willing to participate in a stake holder review process, the OOTB search for user on a Setup participant tab, takes atleast 10 to 15 seconds even when the system is tuned.
The reason being, the OOTB code, first collects the entire memberlist belonging to the specified resourcepool for the workflow task. Then it finds whether the user being searched belongs to the memberlist specified in the resource pool.
There should be some sort of preference or entry by which we can override this behaviour to make the search on user faster, so that the system does not perform the above check.
